// SPDX-License-Identifier: GPL-2.0 /* * Memory Migration functionality - linux/mm/migrate.c * * Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter * * Page migration was first developed in the context of the memory hotplug * project. The main authors of the migration code are: * * IWAMOTO Toshihiro * Hirokazu Takahashi * Dave Hansen * Christoph Lameter */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "internal.h" int isolate_movable_page(struct page *page, isolate_mode_t mode) { struct address_space *mapping; /* * Avoid burning cycles with pages that are yet under __free_pages(), * or just got freed under us. * * In case we 'win' a race for a movable page being freed under us and * raise its refcount preventing __free_pages() from doing its job * the put_page() at the end of this block will take care of * release this page, thus avoiding a nasty leakage. */ if (unlikely(!get_page_unless_zero(page))) goto out; /* * Check PageMovable before holding a PG_lock because page's owner * assumes anybody doesn't touch PG_lock of newly allocated page * so unconditionally grabbing the lock ruins page's owner side. */ if (unlikely(!__PageMovable(page))) goto out_putpage; /* * As movable pages are not isolated from LRU lists, concurrent * compaction threads can race against page migration functions * as well as race against the releasing a page. * * In order to avoid having an already isolated movable page * being (wrongly) re-isolated while it is under migration, * or to avoid attempting to isolate pages being released, * lets be sure we have the page lock * before proceeding with the movable page isolation steps. */ if (unlikely(!trylock_page(page))) goto out_putpage; if (!PageMovable(page) || PageIsolated(page)) goto out_no_isolated; mapping = page_mapping(page); VM_BUG_ON_PAGE(!mapping, page); if (!mapping->a_ops->isolate_page(page, mode)) goto out_no_isolated; /* Driver shouldn't use PG_isolated bit of page->flags */ WARN_ON_ONCE(PageIsolated(page)); SetPageIsolated(page); unlock_page(page); return 0; out_no_isolated: unlock_page(page); out_putpage: put_page(page); out: return -EBUSY; } static void putback_movable_page(struct page *page) { struct address_space *mapping; mapping = page_mapping(page); mapping->a_ops->putback_page(page); ClearPageIsolated(page); } /* * Put previously isolated pages back onto the appropriate lists * from where they were once taken off for compaction/migration. * * This function shall be used whenever the isolated pageset has been * built from lru, balloon, hugetlbfs page. See isolate_migratepages_range() * and isolate_huge_page(). */ void putback_movable_pages(struct list_head *l) { struct page *page; struct page *page2; list_for_each_entry_safe(page, page2, l, lru) { if (unlikely(PageHuge(page))) { putback_active_hugepage(page); continue; } list_del(&page->lru); /* * We isolated non-lru movable page so here we can use * __PageMovable because LRU page's mapping cannot have * PAGE_MAPPING_MOVABLE. */ if (unlikely(__PageMovable(page))) { VM_BUG_ON_PAGE(!PageIsolated(page), page); lock_page(page); if (PageMovable(page)) putback_movable_page(page); else ClearPageIsolated(page); unlock_page(page); put_page(page); } else { mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON + page_is_file_lru(page), -thp_nr_pages(page)); putback_lru_page(page); } } } /* * Restore a potential migration pte to a working pte entry */ static bool remove_migration_pte(struct folio *folio, struct vm_area_struct *vma, unsigned long addr, void *old) { DEFINE_FOLIO_VMA_WALK(pvmw, old, vma, addr, PVMW_SYNC | PVMW_MIGRATION); while (page_vma_mapped_walk(&pvmw)) { pte_t pte; swp_entry_t entry; struct page *new; unsigned long idx = 0; /* pgoff is invalid for ksm pages, but they are never large */ if (folio_test_large(folio) && !folio_test_hugetlb(folio)) idx = linear_page_index(vma, pvmw.address) - pvmw.pgoff; new = folio_page(folio, idx); #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION /* PMD-mapped THP migration entry */ if (!pvmw.pte) { VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) || !folio_test_pmd_mappable(folio), folio); remove_migration_pmd(&pvmw, new); continue; } #endif folio_get(folio); pte = pte_mkold(mk_pte(new, READ_ONCE(vma->vm_page_prot))); if (pte_swp_soft_dirty(*pvmw.pte)) pte = pte_mksoft_dirty(pte); /* * Recheck VMA as permissions can change since migration started */ entry = pte_to_swp_entry(*pvmw.pte); if (is_writable_migration_entry(entry)) pte = maybe_mkwrite(pte, vma); else if (pte_swp_uffd_wp(*pvmw.pte)) pte = pte_mkuffd_wp(pte); if (unlikely(is_device_private_page(new))) { if (pte_write(pte)) entry = make_writable_device_private_entry( page_to_pfn(new)); else entry = make_readable_device_private_entry( page_to_pfn(new)); pte = swp_entry_to_pte(entry); if (pte_swp_soft_dirty(*pvmw.pte)) pte = pte_swp_mksoft_dirty(pte); if (pte_swp_uffd_wp(*pvmw.pte)) pte = pte_swp_mkuffd_wp(pte); } #ifdef CONFIG_HUGETLB_PAGE if (folio_test_hugetlb(folio)) { unsigned int shift = huge_page_shift(hstate_vma(vma)); pte = pte_mkhuge(pte); pte = arch_make_huge_pte(pte, shift, vma->vm_flags); if (folio_test_anon(folio)) hugepage_add_anon_rmap(new, vma, pvmw.address); else page_dup_file_rmap(new, true); set_huge_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte); } else #endif { if (folio_test_anon(folio)) page_add_anon_rmap(new, vma, pvmw.address, false); else page_add_file_rmap(new, vma, false); set_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte); } if (vma->vm_flags & VM_LOCKED) mlock_page_drain_local(); trace_remove_migration_pte(pvmw.address, pte_val(pte), compound_order(new)); /* No need to invalidate - it was non-present before */ update_mmu_cache(vma, pvmw.address, pvmw.pte); } return true; } /* * Get rid of all migration entries and replace them by * references to the indicated page. */ void remove_migration_ptes(struct folio *src, struct folio *dst, bool locked) { struct rmap_walk_control rwc = { .rmap_one = remove_migration_pte, .arg = src, }; if (locked) rmap_walk_locked(dst, &rwc); else rmap_walk(dst, &rwc); } /* * Something used the pte of a page under migration. We need to * get to the page and wait until migration is finished. * When we return from this function the fault will be retried. */ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep, spinlock_t *ptl) { pte_t pte; swp_entry_t entry; spin_lock(ptl); pte = *ptep; if (!is_swap_pte(pte)) goto out; entry = pte_to_swp_entry(pte); if (!is_migration_entry(entry)) goto out; migration_entry_wait_on_locked(entry, ptep, ptl); return; out: pte_unmap_unlock(ptep, ptl); } void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd, unsigned long address) { spinlock_t *ptl = pte_lockptr(mm, pmd); pte_t *ptep = pte_offset_map(pmd, address); __migration_entry_wait(mm, ptep, ptl); } void migration_entry_wait_huge(struct vm_area_struct *vma, struct mm_struct *mm, pte_t *pte) { spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), mm, pte); __migration_entry_wait(mm, pte, ptl); } #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd) { spinlock_t *ptl; ptl = pmd_lock(mm, pmd); if (!is_pmd_migration_entry(*pmd)) goto unlock; migration_entry_wait_on_locked(pmd_to_swp_entry(*pmd), NULL, ptl); return; unlock: spin_unlock(ptl); } #endif static int expected_page_refs(struct address_space *mapping, struct page *page) { int expected_count = 1; if (mapping) expected_count += compound_nr(page) + page_has_private(page); return expected_count; } /* * Replace the page in the mapping. * * The number of remaining references must be: * 1 for anonymous pages without a mapping * 2 for pages with a mapping * 3 for pages with a mapping and PagePrivate/PagePrivate2 set. */ int folio_migrate_mapping(struct address_space *mapping, struct folio *newfolio, struct folio *folio, int extra_count) { XA_STATE(xas, &mapping->i_pages, folio_index(folio)); struct zone *oldzone, *newzone; int dirty; int expected_count = expected_page_refs(mapping, &folio->page) + extra_count; long nr = folio_nr_pages(folio); if (!mapping) { /* Anonymous page without mapping */ if (folio_ref_count(folio) != expected_count) return -EAGAIN; /* No turning back from here */ newfolio->index = folio->index; newfolio->mapping = folio->mapping; if (folio_test_swapbacked(folio)) __folio_set_swapbacked(newfolio); return MIGRATEPAGE_SUCCESS; } oldzone = folio_zone(folio); newzone = folio_zone(newfolio); xas_lock_irq(&xas); if (!folio_ref_freeze(folio, expected_count)) { xas_unlock_irq(&xas); return -EAGAIN; } /* * Now we know that no one else is looking at the folio: * no turning back from here. */ newfolio->index = folio->index; newfolio->mapping = folio->mapping; folio_ref_add(newfolio, nr); /* add cache reference */ if (folio_test_swapbacked(folio)) { __folio_set_swapbacked(newfolio); if (folio_test_swapcache(folio)) { folio_set_swapcache(newfolio); newfolio->private = folio_get_private(folio); } } else { VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio); } /* Move dirty while page refs frozen and newpage not yet exposed */ dirty = folio_test_dirty(folio); if (dirty) { folio_clear_dirty(folio); folio_set_dirty(newfolio); } xas_store(&xas, newfolio); /* * Drop cache reference from old page by unfreezing * to one less reference. * We know this isn't the last reference. */ folio_ref_unfreeze(folio, expected_count - nr); xas_unlock(&xas); /* Leave irq disabled to prevent preemption while updating stats */ /* * If moved to a different zone then also account * the page for that zone. Other VM counters will be * taken care of when we establish references to the * new page and drop references to the old page. * * Note that anonymous pages are accounted for * via NR_FILE_PAGES and NR_ANON_MAPPED if they * are mapped to swap space. */ if (newzone != oldzone) { struct lruvec *old_lruvec, *new_lruvec; struct mem_cgroup *memcg; memcg = folio_memcg(folio); old_lruvec = mem_cgroup_lruvec(memcg, oldzone->zone_pgdat); new_lruvec = mem_cgroup_lruvec(memcg, newzone->zone_pgdat); __mod_lruvec_state(old_lruvec, NR_FILE_PAGES, -nr); __mod_lruvec_state(new_lruvec, NR_FILE_PAGES, nr); if (folio_test_swapbacked(folio) && !folio_test_swapcache(folio)) { __mod_lruvec_state(old_lruvec, NR_SHMEM, -nr); __mod_lruvec_state(new_lruvec, NR_SHMEM, nr); } #ifdef CONFIG_SWAP if (folio_test_swapcache(folio)) { __mod_lruvec_state(old_lruvec, NR_SWAPCACHE, -nr); __mod_lruvec_state(new_lruvec, NR_SWAPCACHE, nr); } #endif if (dirty && mapping_can_writeback(mapping)) { __mod_lruvec_state(old_lruvec, NR_FILE_DIRTY, -nr); __mod_zone_page_state(oldzone, NR_ZONE_WRITE_PENDING, -nr); __mod_lruvec_state(new_lruvec, NR_FILE_DIRTY, nr); __mod_zone_page_state(newzone, NR_ZONE_WRITE_PENDING, nr); } } local_irq_enable(); return MIGRATEPAGE_SUCCESS; } EXPORT_SYMBOL(folio_migrate_mapping); /* * The expected number of remaining references is the same as that * of folio_migrate_mapping(). */ int migrate_huge_page_move_mapping(struct address_space *mapping, struct page *newpage, struct page *page) { XA_STATE(xas, &mapping->i_pages, page_index(page)); int expected_count; xas_lock_irq(&xas); expected_count = 2 + page_has_private(page); if (!page_ref_freeze(page, expected_count)) { xas_unlock_irq(&xas); return -EAGAIN; } newpage->index = page->index; newpage->mapping = page->mapping; get_page(newpage); xas_store(&xas, newpage); page_ref_unfreeze(page, expected_count - 1); xas_unlock_irq(&xas); return MIGRATEPAGE_SUCCESS; } /* * Copy the flags and some other ancillary information */ void folio_migrate_flags(struct folio *newfolio, struct folio *folio) { int cpupid; if (folio_test_error(folio)) folio_set_error(newfolio); if (folio_test_referenced(folio)) folio_set_referenced(newfolio); if (folio_test_uptodate(folio)) folio_mark_uptodate(newfolio); if (folio_test_clear_active(folio)) { VM_BUG_ON_FOLIO(folio_test_unevictable(folio), folio); folio_set_active(newfolio); } else if (folio_test_clear_unevictable(folio)) folio_set_unevictable(newfolio); if (folio_test_workingset(folio)) folio_set_workingset(newfolio); if (folio_test_checked(folio)) folio_set_checked(newfolio); if (folio_test_mappedtodisk(folio)) folio_set_mappedtodisk(newfolio); /* Move dirty on pages not done by folio_migrate_mapping() */ if (folio_test_dirty(folio)) folio_set_dirty(newfolio); if (folio_test_young(folio)) folio_set_young(newfolio); if (folio_test_idle(folio)) folio_set_idle(newfolio); /* * Copy NUMA information to the new page, to prevent over-eager * future migrations of this same page. */ cpupid = page_cpupid_xchg_last(&folio->page, -1); page_cpupid_xchg_last(&newfolio->page, cpupid); folio_migrate_ksm(newfolio, folio); /* * Please do not reorder this without considering how mm/ksm.c's * get_ksm_page() depends upon ksm_migrate_page() and PageSwapCache(). */ if (folio_test_swapcache(folio)) folio_clear_swapcache(folio); folio_clear_private(folio); /* page->private contains hugetlb specific flags */ if (!folio_test_hugetlb(folio)) folio->private = NULL; /* * If any waiters have accumulated on the new page then * wake them up. */ if (folio_test_writeback(newfolio)) folio_end_writeback(newfolio); /* * PG_readahead shares the same bit with PG_reclaim. The above * end_page_writeback() may clear PG_readahead mistakenly, so set the * bit after that. */ if (folio_test_readahead(folio)) folio_set_readahead(newfolio); folio_copy_owner(newfolio, folio); if (!folio_test_hugetlb(folio)) mem_cgroup_migrate(folio, newfolio); } EXPORT_SYMBOL(folio_migrate_flags); void folio_migrate_copy(struct folio *newfolio, struct folio *folio) { folio_copy(newfolio, folio); folio_migrate_flags(newfolio, folio); } EXPORT_SYMBOL(folio_migrate_copy); /************************************************************ * Migration functions ***********************************************************/ /* * Common logic to directly migrate a single LRU page suitable for * pages that do not use PagePrivate/PagePrivate2. * * Pages are locked upon entry and exit. */ int migrate_page(struct address_space *mapping, struct page *newpage, struct page *page, enum migrate_mode mode) { struct folio *newfolio = page_folio(newpage); struct folio *folio = page_folio(page); int rc; BUG_ON(folio_test_writeback(folio)); /* Writeback must be complete */ rc = folio_migrate_mapping(mapping, newfolio, folio, 0); if (rc != MIGRATEPAGE_SUCCESS) return rc; if (mode != MIGRATE_SYNC_NO_COPY) folio_migrate_copy(newfolio, folio); else folio_migrate_flags(newfolio, folio); return MIGRATEPAGE_SUCCESS; } EXPORT_SYMBOL(migrate_page); #ifdef CONFIG_BLOCK /* Returns true if all buffers are successfully locked */ static bool buffer_migrate_lock_buffers(struct buffer_head *head, enum migrate_mode mode) { struct buffer_head *bh = head; /* Simple case, sync compaction */ if (mode != MIGRATE_ASYNC) { do { lock_buffer(bh); bh = bh->b_this_page; } while (bh != head); return true; } /* async case, we cannot block on lock_buffer so use trylock_buffer */ do { if (!trylock_buffer(bh)) { /* * We failed to lock the buffer and cannot stall in * async migration. Release the taken locks */ struct buffer_head *failed_bh = bh; bh = head; while (bh != failed_bh) { unlock_buffer(bh); bh = bh->b_this_page; } return false; } bh = bh->b_this_page; } while (bh != head); return true; } static int __buffer_migrate_page(struct address_space *mapping, struct page *newpage, struct page *page, enum migrate_mode mode, bool check_refs) { struct buffer_head *bh, *head; int rc; int expected_count; if (!page_has_buffers(page)) return migrate_page(mapping, newpage, page, mode); /* Check whether page does not have extra refs before we do more work */ expected_count = expected_page_refs(mapping, page); if (page_count(page) != expected_count) return -EAGAIN; head = page_buffers(page); if (!buffer_migrate_lock_buffers(head, mode)) return -EAGAIN; if (check_refs) { bool busy; bool invalidated = false; recheck_buffers: busy = false; spin_lock(&mapping->private_lock); bh = head; do { if (atomic_read(&bh->b_count)) { busy = true; break; } bh = bh->b_this_page; } while (bh != head); if (busy) { if (invalidated) { rc = -EAGAIN; goto unlock_buffers; } spin_unlock(&mapping->private_lock); invalidate_bh_lrus(); invalidated = true; goto recheck_buffers; } } rc = migrate_page_move_mapping(mapping, newpage, page, 0); if (rc != MIGRATEPAGE_SUCCESS) goto unlock_buffers; attach_page_private(newpage, detach_page_private(page)); bh = head; do { set_bh_page(bh, newpage, bh_offset(bh)); bh = bh->b_this_page; } while (bh != head); if (mode != MIGRATE_SYNC_NO_COPY) migrate_page_copy(newpage, page); else migrate_page_states(newpage, page); rc = MIGRATEPAGE_SUCCESS; unlock_buffers: if (check_refs) spin_unlock(&mapping->private_lock); bh = head; do { unlock_buffer(bh); bh = bh->b_this_page; } while (bh != head); return rc; } /* * Migration function for pages with buffers. This function can only be used * if the underlying filesystem guarantees that no other references to "page" * exist. For example attached buffer heads are accessed only under page lock. */ int buffer_migrate_page(struct address_space *mapping, struct page *newpage, struct page *page, enum migrate_mode mode) { return __buffer_migrate_page(mapping, newpage, page, mode, false); } EXPORT_SYMBOL(buffer_migrate_page); /* * Same as above except that this variant is more careful and checks that there * are also no buffer head references. This function is the right one for * mappings where buffer heads are directly looked up and referenced (such as * block device mappings). */ int buffer_migrate_page_norefs(struct address_space *mapping, struct page *newpage, struct page *page, enum migrate_mode mode) { return __buffer_migrate_page(mapping, newpage, page, mode, true); } #endif /* * Writeback a page to clean the dirty state */ static int writeout(struct address_space *mapping, struct page *page) { struct folio *folio = page_folio(page); struct writeback_control wbc = { .sync_mode = WB_SYNC_NONE, .nr_to_write = 1, .range_start = 0, .range_end = LLONG_MAX, .for_reclaim = 1 }; int rc; if (!mapping->a_ops->writepage) /* No write method for the address space */ return -EINVAL; if (!clear_page_dirty_for_io(page)) /* Someone else already triggered a write */ return -EAGAIN; /* * A dirty page may imply that the underlying filesystem has * the page on some queue. So the page must be clean for * migration. Writeout may mean we loose the lock and the * page state is no longer what we checked for earlier. * At this point we know that the migration attempt cannot * be successful. */ remove_migration_ptes(folio, folio, false); rc = mapping->a_ops->writepage(page, &wbc); if (rc != AOP_WRITEPAGE_ACTIVATE) /* unlocked. Relock */ lock_page(page); return (rc < 0) ? -EIO : -EAGAIN; } /* * Default handling if a filesystem does not provide a migration function. */ static int fallback_migrate_page(struct address_space *mapping, struct page *newpage, struct page *page, enum migrate_mode mode) { if (PageDirty(page)) { /* Only writeback pages in full synchronous migration */ switch (mode) { case MIGRATE_SYNC: case MIGRATE_SYNC_NO_COPY: break; default: return -EBUSY; } return writeout(mapping, page); } /* * Buffers may be managed in a filesystem specific way. * We must have no buffers or drop them. */ if (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL)) return mode == MIGRATE_SYNC ? -EAGAIN : -EBUSY; return migrate_page(mapping, newpage, page, mode); } /* * Move a page to a newly allocated page * The page is locked and all ptes have been successfully removed. * * The new page will have replaced the old page if this function * is successful. * * Return value: * < 0 - error code * MIGRATEPAGE_SUCCESS - success */ static int move_to_new_page(struct page *newpage, struct page *page, enum migrate_mode mode) { struct address_space *mapping; int rc = -EAGAIN; bool is_lru = !__PageMovable(page); VM_BUG_ON_PAGE(!PageLocked(page), page); VM_BUG_ON_PAGE(!PageLocked(newpage), newpage); mapping = page_mapping(page); if (likely(is_lru)) { if (!mapping) rc = migrate_page(mapping, newpage, page, mode); else if (mapping->a_ops->migratepage) /* * Most pages have a mapping and most filesystems * provide a migratepage callback. Anonymous pages * are part of swap space which also has its own * migratepage callback. This is the most common path * for page migration. */ rc = mapping->a_ops->migratepage(mapping, newpage, page, mode); else rc = fallback_migrate_page(mapping, newpage, page, mode); } else { /* * In case of non-lru page, it could be released after * isolation step. In that case, we shouldn't try migration. */ VM_BUG_ON_PAGE(!PageIsolated(page), page); if (!PageMovable(page)) { rc = MIGRATEPAGE_SUCCESS; ClearPageIsolated(page); goto out; } rc = mapping->a_ops->migratepage(mapping, newpage, page, mode); WARN_ON_ONCE(rc == MIGRATEPAGE_SUCCESS && !PageIsolated(page)); } /* * When successful, old pagecache page->mapping must be cleared before * page is freed; but stats require that PageAnon be left as PageAnon. */ if (rc == MIGRATEPAGE_SUCCESS) { if (__PageMovable(page)) { VM_BUG_ON_PAGE(!PageIsolated(page), page); /* * We clear PG_movable under page_lock so any compactor * cannot try to migrate this page. */ ClearPageIsolated(page); } /* * Anonymous and movable page->mapping will be cleared by * free_pages_prepare so don't reset it here for keeping * the type to work PageAnon, for example. */ if (!PageMappingFlags(page)) page->mapping = NULL; if (likely(!is_zone_device_page(newpage))) flush_dcache_folio(page_folio(newpage)); } out: return rc; } static int __unmap_and_move(struct page *page, struct page *newpage, int force, enum migrate_mode mode) { struct folio *folio = page_folio(page); struct folio *dst = page_folio(newpage); int rc = -EAGAIN; bool page_was_mapped = false; struct anon_vma *anon_vma = NULL; bool is_lru = !__PageMovable(page); if (!trylock_page(page)) { if (!force || mode == MIGRATE_ASYNC) goto out; /* * It's not safe for direct compaction to call lock_page. * For example, during page readahead pages are added locked * to the LRU. Later, when the IO completes the pages are * marked uptodate and unlocked. However, the queueing * could be merging multiple pages for one bio (e.g. * mpage_readahead). If an allocation happens for the * second or third page, the process can end up locking * the same page twice and deadlocking. Rather than * trying to be clever about what pages can be locked, * avoid the use of lock_page for direct compaction * altogether. */ if (current->flags & PF_MEMALLOC) goto out; lock_page(page); } if (PageWriteback(page)) { /* * Only in the case of a full synchronous migration is it * necessary to wait for PageWriteback. In the async case, * the retry loop is too short and in the sync-light case, * the overhead of stalling is too much */ switch (mode) { case MIGRATE_SYNC: case MIGRATE_SYNC_NO_COPY: break; default: rc = -EBUSY; goto out_unlock; } if (!force) goto out_unlock; wait_on_page_writeback(page); } /* * By try_to_migrate(), page->mapcount goes down to 0 here. In this case, * we cannot notice that anon_vma is freed while we migrates a page. * This get_anon_vma() delays freeing anon_vma pointer until the end * of migration. File cache pages are no problem because of page_lock() * File Caches may use write_page() or lock_page() in migration, then, * just care Anon page here. * * Only page_get_anon_vma() understands the subtleties of * getting a hold on an anon_vma from outside one of its mms. * But if we cannot get anon_vma, then we won't need it anyway, * because that implies that the anon page is no longer mapped * (and cannot be remapped so long as we hold the page lock). */ if (PageAnon(page) && !PageKsm(page)) anon_vma = page_get_anon_vma(page); /* * Block others from accessing the new page when we get around to * establishing additional references. We are usually the only one * holding a reference to newpage at this point. We used to have a BUG * here if trylock_page(newpage) fails, but would like to allow for * cases where there might be a race with the previous use of newpage. * This is much like races on refcount of oldpage: just don't BUG(). */ if (unlikely(!trylock_page(newpage))) goto out_unlock; if (unlikely(!is_lru)) { rc = move_to_new_page(newpage, page, mode); goto out_unlock_both; } /* * Corner case handling: * 1. When a new swap-cache page is read into, it is added to the LRU * and treated as swapcache but it has no rmap yet. * Calling try_to_unmap() against a page->mapping==NULL page will * trigger a BUG. So handle it here. * 2. An orphaned page (see truncate_cleanup_page) might have * fs-private metadata. The page can be picked up due to memory * offlining. Everywhere else except page reclaim, the page is * invisible to the vm, so the page can not be migrated. So try to * free the metadata, so the page can be freed. */ if (!page->mapping) { VM_BUG_ON_PAGE(PageAnon(page), page); if (page_has_private(page)) { try_to_free_buffers(page); goto out_unlock_both; } } else if (page_mapped(page)) { /* Establish migration ptes */ VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma, page); try_to_migrate(folio, 0); page_was_mapped = true; } if (!page_mapped(page)) rc = move_to_new_page(newpage, page, mode); /* * When successful, push newpage to LRU immediately: so that if it * turns out to be an mlocked page, remove_migration_ptes() will * automatically build up the correct newpage->mlock_count for it. * * We would like to do something similar for the old page, when * unsuccessful, and other cases when a page has been temporarily * isolated from the unevictable LRU: but this case is the easiest. */ if (rc == MIGRATEPAGE_SUCCESS) { lru_cache_add(newpage); if (page_was_mapped) lru_add_drain(); } if (page_was_mapped) remove_migration_ptes(folio, rc == MIGRATEPAGE_SUCCESS ? dst : folio, false); out_unlock_both: unlock_page(newpage); out_unlock: /* Drop an anon_vma reference if we took one */ if (anon_vma) put_anon_vma(anon_vma); unlock_page(page); out: /* * If migration is successful, decrease refcount of the newpage, * which will not free the page because new page owner increased * refcounter. */ if (rc == MIGRATEPAGE_SUCCESS) put_page(newpage); return rc; } /* * Obtain the lock on page, remove all ptes and migrate the page * to the newly allocated page in newpage. */ static int unmap_and_move(new_page_t get_new_page, free_page_t put_new_page, unsigned long private, struct page *page, int force, enum migrate_mode mode, enum migrate_reason reason, struct list_head *ret) { int rc = MIGRATEPAGE_SUCCESS; struct page *newpage = NULL; if (!thp_migration_supported() && PageTransHuge(page)) return -ENOSYS; if (page_count(page) == 1) { /* page was freed from under us. So we are done. */ ClearPageActive(page); ClearPageUnevictable(page); if (unlikely(__PageMovable(page))) { lock_page(page); if (!PageMovable(page)) ClearPageIsolated(page); unlock_page(page); } goto out; } newpage = get_new_page(page, private); if (!newpage) return -ENOMEM; rc = __unmap_and_move(page, newpage, force, mode); if (rc == MIGRATEPAGE_SUCCESS) set_page_owner_migrate_reason(newpage, reason); out: if (rc != -EAGAIN) { /* * A page that has been migrated has all references * removed and will be freed. A page that has not been * migrated will have kept its references and be restored. */ list_del(&page->lru); } /* * If migration is successful, releases reference grabbed during * isolation. Otherwise, restore the page to right list unless * we want to retry. */ if (rc == MIGRATEPAGE_SUCCESS) { /* * Compaction can migrate also non-LRU pages which are * not accounted to NR_ISOLATED_*. They can be recognized * as __PageMovable */ if (likely(!__PageMovable(page))) mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON + page_is_file_lru(page), -thp_nr_pages(page)); if (reason != MR_MEMORY_FAILURE) /* * We release the page in page_handle_poison. */ put_page(page); } else { if (rc != -EAGAIN) list_add_tail(&page->lru, ret); if (put_new_page) put_new_page(newpage, private); else put_page(newpage); } return rc; } /* * Counterpart of unmap_and_move_page() for hugepage migration. * * This function doesn't wait the completion of hugepage I/O * because there is no race between I/O and migration for hugepage. * Note that currently hugepage I/O occurs only in direct I/O * where no lock is held and PG_writeback is irrelevant, * and writeback status of all subpages are counted in the reference * count of the head page (i.e. if all subpages of a 2MB hugepage are * under direct I/O, the reference of the head page is 512 and a bit more.) * This means that when we try to migrate hugepage whose subpages are * doing direct I/O, some references remain after try_to_unmap() and * hugepage migration fails without data corruption. * * There is also no race when direct I/O is issued on the page under migration, * because then pte is replaced with migration swap entry and direct I/O code * will wait in the page fault for migration to complete. */ static int unmap_and_move_huge_page(new_page_t get_new_page, free_page_t put_new_page, unsigned long private, struct page *hpage, int force, enum migrate_mode mode, int reason, struct list_head *ret) { struct folio *dst, *src = page_folio(hpage); int rc = -EAGAIN; int page_was_mapped = 0; struct page *new_hpage; struct anon_vma *anon_vma = NULL; struct address_space *mapping = NULL; /* * Migratability of hugepages depends on architectures and their size. * This check is necessary because some callers of hugepage migration * like soft offline and memory hotremove don't walk through page * tables or check whether the hugepage is pmd-based or not before * kicking migration. */ if (!hugepage_migration_supported(page_hstate(hpage))) { list_move_tail(&hpage->lru, ret); return -ENOSYS; } if (page_count(hpage) == 1) { /* page was freed from under us. So we are done. */ putback_active_hugepage(hpage); return MIGRATEPAGE_SUCCESS; } new_hpage = get_new_page(hpage, private); if (!new_hpage) return -ENOMEM; dst = page_folio(new_hpage); if (!trylock_page(hpage)) { if (!force) goto out; switch (mode) { case MIGRATE_SYNC: case MIGRATE_SYNC_NO_COPY: break; default: goto out; } lock_page(hpage); } /* * Check for pages which are in the process of being freed. Without * page_mapping() set, hugetlbfs specific move page routine will not * be called and we could leak usage counts for subpools. */ if (hugetlb_page_subpool(hpage) && !page_mapping(hpage)) { rc = -EBUSY; goto out_unlock; } if (PageAnon(hpage)) anon_vma = page_get_anon_vma(hpage); if (unlikely(!trylock_page(new_hpage))) goto put_anon; if (page_mapped(hpage)) { enum ttu_flags ttu = 0; if (!PageAnon(hpage)) { /* * In shared mappings, try_to_unmap could potentially * call huge_pmd_unshare. Because of this, take * semaphore in write mode here and set TTU_RMAP_LOCKED * to let lower levels know we have taken the lock. */ mapping = hugetlb_page_mapping_lock_write(hpage); if (unlikely(!mapping)) goto unlock_put_anon; ttu = TTU_RMAP_LOCKED; } try_to_migrate(src, ttu); page_was_mapped = 1; if (ttu & TTU_RMAP_LOCKED) i_mmap_unlock_write(mapping); } if (!page_mapped(hpage)) rc = move_to_new_page(new_hpage, hpage, mode); if (page_was_mapped) remove_migration_ptes(src, rc == MIGRATEPAGE_SUCCESS ? dst : src, false); unlock_put_anon: unlock_page(new_hpage); put_anon: if (anon_vma) put_anon_vma(anon_vma); if (rc == MIGRATEPAGE_SUCCESS) { move_hugetlb_state(hpage, new_hpage, reason); put_new_page = NULL; } out_unlock: unlock_page(hpage); out: if (rc == MIGRATEPAGE_SUCCESS) putback_active_hugepage(hpage); else if (rc != -EAGAIN) list_move_tail(&hpage->lru, ret); /* * If migration was not successful and there's a freeing callback, use * it. Otherwise, put_page() will drop the reference grabbed during * isolation. */ if (put_new_page) put_new_page(new_hpage, private); else putback_active_hugepage(new_hpage); return rc; } static inline int try_split_thp(struct page *page, struct page **page2, struct list_head *from) { int rc = 0; lock_page(page); rc = split_huge_page_to_list(page, from); unlock_page(page); if (!rc) list_safe_reset_next(page, *page2, lru); return rc; } /* * migrate_pages - migrate the pages specified in a list, to the free pages * supplied as the target for the page migration * * @from: The list of pages to be migrated. * @get_new_page: The function used to allocate free pages to be used * as the target of the page migration. * @put_new_page: The function used to free target pages if migration * fails, or NULL if no special handling is necessary. * @private: Private data to be passed on to get_new_page() * @mode: The migration mode that specifies the constraints for * page migration, if any. * @reason: The reason for page migration. * @ret_succeeded: Set to the number of normal pages migrated successfully if * the caller passes a non-NULL pointer. * * The function returns after 10 attempts or if no pages are movable any more * because the list has become empty or no retryable pages exist any more. * It is caller's responsibility to call putback_movable_pages() to return pages * to the LRU or free list only if ret != 0. * * Returns the number of {normal page, THP, hugetlb} that were not migrated, or * an error code. The number of THP splits will be considered as the number of * non-migrated THP, no matter how many subpages of the THP are migrated successfully. */ int migrate_pages(struct list_head *from, new_page_t get_new_page, free_page_t put_new_page, unsigned long private, enum migrate_mode mode, int reason, unsigned int *ret_succeeded) { int retry = 1; int thp_retry = 1; int nr_failed = 0; int nr_failed_pages = 0; int nr_succeeded = 0; int nr_thp_succeeded = 0; int nr_thp_failed = 0; int nr_thp_split = 0; int pass = 0; bool is_thp = false; struct page *page; struct page *page2; int rc, nr_subpages; LIST_HEAD(ret_pages); LIST_HEAD(thp_split_pages); bool nosplit = (reason == MR_NUMA_MISPLACED); bool no_subpage_counting = false; trace_mm_migrate_pages_start(mode, reason); thp_subpage_migration: for (pass = 0; pass < 10 && (retry || thp_retry); pass++) { retry = 0; thp_retry = 0; list_for_each_entry_safe(page, page2, from, lru) { retry: /* * THP statistics is based on the source huge page. * Capture required information that might get lost * during migration. */ is_thp = PageTransHuge(page) && !PageHuge(page); nr_subpages = compound_nr(page); cond_resched(); if (PageHuge(page)) rc = unmap_and_move_huge_page(get_new_page, put_new_page, private, page, pass > 2, mode, reason, &ret_pages); else rc = unmap_and_move(get_new_page, put_new_page, private, page, pass > 2, mode, reason, &ret_pages); /* * The rules are: * Success: non hugetlb page will be freed, hugetlb * page will be put back * -EAGAIN: stay on the from list * -ENOMEM: stay on the from list * Other errno: put on ret_pages list then splice to * from list */ switch(rc) { /* * THP migration might be unsupported or the * allocation could've failed so we should * retry on the same page with the THP split * to base pages. * * Head page is retried immediately and tail * pages are added to the tail of the list so * we encounter them after the rest of the list * is processed. */ case -ENOSYS: /* THP migration is unsupported */ if (is_thp) { nr_thp_failed++; if (!try_split_thp(page, &page2, &thp_split_pages)) { nr_thp_split++; goto retry; } /* Hugetlb migration is unsupported */ } else if (!no_subpage_counting) { nr_failed++; } nr_failed_pages += nr_subpages; break; case -ENOMEM: /* * When memory is low, don't bother to try to migrate * other pages, just exit. * THP NUMA faulting doesn't split THP to retry. */ if (is_thp && !nosplit) { nr_thp_failed++; if (!try_split_thp(page, &page2, &thp_split_pages)) { nr_thp_split++; goto retry; } } else if (!no_subpage_counting) { nr_failed++; } nr_failed_pages += nr_subpages; /* * There might be some subpages of fail-to-migrate THPs * left in thp_split_pages list. Move them back to migration * list so that they could be put back to the right list by * the caller otherwise the page refcnt will be leaked. */ list_splice_init(&thp_split_pages, from); nr_thp_failed += thp_retry; goto out; case -EAGAIN: if (is_thp) thp_retry++; else retry++; break; case MIGRATEPAGE_SUCCESS: nr_succeeded += nr_subpages; if (is_thp) nr_thp_succeeded++; break; default: /* * Permanent failure (-EBUSY, etc.): * unlike -EAGAIN case, the failed page is * removed from migration page list and not * retried in the next outer loop. */ if (is_thp) nr_thp_failed++; else if (!no_subpage_counting) nr_failed++; nr_failed_pages += nr_subpages; break; } } } nr_failed += retry; nr_thp_failed += thp_retry; /* * Try to migrate subpages of fail-to-migrate THPs, no nr_failed * counting in this round, since all subpages of a THP is counted * as 1 failure in the first round. */ if (!list_empty(&thp_split_pages)) { /* * Move non-migrated pages (after 10 retries) to ret_pages * to avoid migrating them again. */ list_splice_init(from, &ret_pages); list_splice_init(&thp_split_pages, from); no_subpage_counting = true; retry = 1; goto thp_subpage_migration; } rc = nr_failed + nr_thp_failed; out: /* * Put the permanent failure page back to migration list, they * will be put back to the right list by the caller. */ list_splice(&ret_pages, from); count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded); count_vm_events(PGMIGRATE_FAIL, nr_failed_pages); count_vm_events(THP_MIGRATION_SUCCESS, nr_thp_succeeded); count_vm_events(THP_MIGRATION_FAIL, nr_thp_failed); count_vm_events(THP_MIGRATION_SPLIT, nr_thp_split); trace_mm_migrate_pages(nr_succeeded, nr_failed_pages, nr_thp_succeeded, nr_thp_failed, nr_thp_split, mode, reason); if (ret_succeeded) *ret_succeeded = nr_succeeded; return rc; } struct page *alloc_migration_target(struct page *page, unsigned long private) { struct folio *folio = page_folio(page); struct migration_target_control *mtc; gfp_t gfp_mask; unsigned int order = 0; struct folio *new_folio = NULL; int nid; int zidx; mtc = (struct migration_target_control *)private; gfp_mask = mtc->gfp_mask; nid = mtc->nid; if (nid == NUMA_NO_NODE) nid = folio_nid(folio); if (folio_test_hugetlb(folio)) { struct hstate *h = page_hstate(&folio->page); gfp_mask = htlb_modify_alloc_mask(h, gfp_mask); return alloc_huge_page_nodemask(h, nid, mtc->nmask, gfp_mask); } if (folio_test_large(folio)) { /* * clear __GFP_RECLAIM to make the migration callback * consistent with regular THP allocations. */ gfp_mask &= ~__GFP_RECLAIM; gfp_mask |= GFP_TRANSHUGE; order = folio_order(folio); } zidx = zone_idx(folio_zone(folio)); if (is_highmem_idx(zidx) || zidx == ZONE_MOVABLE) gfp_mask |= __GFP_HIGHMEM; new_folio = __folio_alloc(gfp_mask, order, nid, mtc->nmask); return &new_folio->page; } #ifdef CONFIG_NUMA static int store_status(int __user *status, int start, int value, int nr) { while (nr-- > 0) { if (put_user(value, status + start)) return -EFAULT; start++; } return 0; } static int do_move_pages_to_node(struct mm_struct *mm, struct list_head *pagelist, int node) { int err; struct migration_target_control mtc = { .nid = node, .gfp_mask = GFP_HIGHUSER_MOVABLE | __GFP_THISNODE, }; err = migrate_pages(pagelist, alloc_migration_target, NULL, (unsigned long)&mtc, MIGRATE_SYNC, MR_SYSCALL, NULL); if (err) putback_movable_pages(pagelist); return err; } /* * Resolves the given address to a struct page, isolates it from the LRU and * puts it to the given pagelist. * Returns: * errno - if the page cannot be found/isolated * 0 - when it doesn't have to be migrated because it is already on the * target node * 1 - when it has been queued */ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr, int node, struct list_head *pagelist, bool migrate_all) { struct vm_area_struct *vma; struct page *page; int err; mmap_read_lock(mm); err = -EFAULT; vma = vma_lookup(mm, addr); if (!vma || !vma_migratable(vma)) goto out; /* FOLL_DUMP to ignore special (like zero) pages */ page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); err = PTR_ERR(page); if (IS_ERR(page)) goto out; err = -ENOENT; if (!page) goto out; err = 0; if (page_to_nid(page) == node) goto out_putpage; err = -EACCES; if (page_mapcount(page) > 1 && !migrate_all) goto out_putpage; if (PageHuge(page)) { if (PageHead(page)) { isolate_huge_page(page, pagelist); err = 1; } } else { struct page *head; head = compound_head(page); err = isolate_lru_page(head); if (err) goto out_putpage; err = 1; list_add_tail(&head->lru, pagelist); mod_node_page_state(page_pgdat(head), NR_ISOLATED_ANON + page_is_file_lru(head), thp_nr_pages(head)); } out_putpage: /* * Either remove the duplicate refcount from * isolate_lru_page() or drop the page ref if it was * not isolated. */ put_page(page); out: mmap_read_unlock(mm); return err; } static int move_pages_and_store_status(struct mm_struct *mm, int node, struct list_head *pagelist, int __user *status, int start, int i, unsigned long nr_pages) { int err; if (list_empty(pagelist)) return 0; err = do_move_pages_to_node(mm, pagelist, node); if (err) { /* * Positive err means the number of failed * pages to migrate. Since we are going to * abort and return the number of non-migrated * pages, so need to include the rest of the * nr_pages that have not been attempted as * well. */ if (err > 0) err += nr_pages - i - 1; return err; } return store_status(status, start, node, i - start); } /* * Migrate an array of page address onto an array of nodes and fill * the corresponding array of status. */ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes, unsigned long nr_pages, const void __user * __user *pages, const int __user *nodes, int __user *status, int flags) { int current_node = NUMA_NO_NODE; LIST_HEAD(pagelist); int start, i; int err = 0, err1; lru_cache_disable(); for (i = start = 0; i < nr_pages; i++) { const void __user *p; unsigned long addr; int node; err = -EFAULT; if (get_user(p, pages + i)) goto out_flush; if (get_user(node, nodes + i)) goto out_flush; addr = (unsigned long)untagged_addr(p); err = -ENODEV; if (node < 0 || node >= MAX_NUMNODES) goto out_flush; if (!node_state(node, N_MEMORY)) goto out_flush; err = -EACCES; if (!node_isset(node, task_nodes)) goto out_flush; if (current_node == NUMA_NO_NODE) { current_node = node; start = i; } else if (node != current_node) { err = move_pages_and_store_status(mm, current_node, &pagelist, status, start, i, nr_pages); if (err) goto out; start = i; current_node = node; } /* * Errors in the page lookup or isolation are not fatal and we simply * report them via status */ err = add_page_for_migration(mm, addr, current_node, &pagelist, flags & MPOL_MF_MOVE_ALL); if (err > 0) { /* The page is successfully queued for migration */ continue; } /* * The move_pages() man page does not have an -EEXIST choice, so * use -EFAULT instead. */ if (err == -EEXIST) err = -EFAULT; /* * If the page is already on the target node (!err), store the * node, otherwise, store the err. */ err = store_status(status, i, err ? : current_node, 1); if (err) goto out_flush; err = move_pages_and_store_status(mm, current_node, &pagelist, status, start, i, nr_pages); if (err) goto out; current_node = NUMA_NO_NODE; } out_flush: /* Make sure we do not overwrite the existing error */ err1 = move_pages_and_store_status(mm, current_node, &pagelist, status, start, i, nr_pages); if (err >= 0) err = err1; out: lru_cache_enable(); return err; } /* * Determine the nodes of an array of pages and store it in an array of status. */ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, const void __user **pages, int *status) { unsigned long i; mmap_read_lock(mm); for (i = 0; i < nr_pages; i++) { unsigned long addr = (unsigned long)(*pages); struct vm_area_struct *vma; struct page *page; int err = -EFAULT; vma = vma_lookup(mm, addr); if (!vma) goto set_status; /* FOLL_DUMP to ignore special (like zero) pages */ page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); err = PTR_ERR(page); if (IS_ERR(page)) goto set_status; if (page) { err = page_to_nid(page); put_page(page); } else { err = -ENOENT; } set_status: *status = err; pages++; status++; } mmap_read_unlock(mm); } static int get_compat_pages_array(const void __user *chunk_pages[], const void __user * __user *pages, unsigned long chunk_nr) { compat_uptr_t __user *pages32 = (compat_uptr_t __user *)pages; compat_uptr_t p; int i; for (i = 0; i < chunk_nr; i++) { if (get_user(p, pages32 + i)) return -EFAULT; chunk_pages[i] = compat_ptr(p); } return 0; } /* * Determine the nodes of a user array of pages and store it in * a user array of status. */ static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages, const void __user * __user *pages, int __user *status) { #define DO_PAGES_STAT_CHUNK_NR 16UL const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR]; int chunk_status[DO_PAGES_STAT_CHUNK_NR]; while (nr_pages) { unsigned long chunk_nr = min(nr_pages, DO_PAGES_STAT_CHUNK_NR); if (in_compat_syscall()) { if (get_compat_pages_array(chunk_pages, pages, chunk_nr)) break; } else { if (copy_from_user(chunk_pages, pages, chunk_nr * sizeof(*chunk_pages))) break; } do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status); if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status))) break; pages += chunk_nr; status += chunk_nr; nr_pages -= chunk_nr; } return nr_pages ? -EFAULT : 0; } static struct mm_struct *find_mm_struct(pid_t pid, nodemask_t *mem_nodes) { struct task_struct *task; struct mm_struct *mm; /* * There is no need to check if current process has the right to modify * the specified process when they are same. */ if (!pid) { mmget(current->mm); *mem_nodes = cpuset_mems_allowed(current); return current->mm; } /* Find the mm_struct */ rcu_read_lock(); task = find_task_by_vpid(pid); if (!task) { rcu_read_unlock(); return ERR_PTR(-ESRCH); } get_task_struct(task); /* * Check if this process has the right to modify the specified * process. Use the regular "ptrace_may_access()" checks. */ if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { rcu_read_unlock(); mm = ERR_PTR(-EPERM); goto out; } rcu_read_unlock(); mm = ERR_PTR(security_task_movememory(task)); if (IS_ERR(mm)) goto out; *mem_nodes = cpuset_mems_allowed(task); mm = get_task_mm(task); out: put_task_struct(task); if (!mm) mm = ERR_PTR(-EINVAL); return mm; } /* * Move a list of pages in the address space of the currently executing * process. */ static int kernel_move_pages(pid_t pid, unsigned long nr_pages, const void __user * __user *pages, const int __user *nodes, int __user *status, int flags) { struct mm_struct *mm; int err; nodemask_t task_nodes; /* Check flags */ if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL)) return -EINVAL; if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE)) return -EPERM; mm = find_mm_struct(pid, &task_nodes); if (IS_ERR(mm)) return PTR_ERR(mm); if (nodes) err = do_pages_move(mm, task_nodes, nr_pages, pages, nodes, status, flags); else err = do_pages_stat(mm, nr_pages, pages, status); mmput(mm); return err; } SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages, const void __user * __user *, pages, const int __user *, nodes, int __user *, status, int, flags) { return kernel_move_pages(pid, nr_pages, pages, nodes, status, flags); } #ifdef CONFIG_NUMA_BALANCING /* * Returns true if this is a safe migration target node for misplaced NUMA * pages. Currently it only checks the watermarks which is crude. */ static bool migrate_balanced_pgdat(struct pglist_data *pgdat, unsigned long nr_migrate_pages) { int z; for (z = pgdat->nr_zones - 1; z >= 0; z--) { struct zone *zone = pgdat->node_zones + z; if (!managed_zone(zone)) continue; /* Avoid waking kswapd by allocating pages_to_migrate pages. */ if (!zone_watermark_ok(zone, 0, high_wmark_pages(zone) + nr_migrate_pages, ZONE_MOVABLE, 0)) continue; return true; } return false; } static struct page *alloc_misplaced_dst_page(struct page *page, unsigned long data) { int nid = (int) data; int order = compound_order(page); gfp_t gfp = __GFP_THISNODE; struct folio *new; if (order > 0) gfp |= GFP_TRANSHUGE_LIGHT; else { gfp |= GFP_HIGHUSER_MOVABLE | __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN; gfp &= ~__GFP_RECLAIM; } new = __folio_alloc_node(gfp, order, nid); return &new->page; } static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page) { int nr_pages = thp_nr_pages(page); int order = compound_order(page); VM_BUG_ON_PAGE(order && !PageTransHuge(page), page); /* Do not migrate THP mapped by multiple processes */ if (PageTransHuge(page) && total_mapcount(page) > 1) return 0; /* Avoid migrating to a node that is nearly full */ if (!migrate_balanced_pgdat(pgdat, nr_pages)) { int z; if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING)) return 0; for (z = pgdat->nr_zones - 1; z >= 0; z--) { if (managed_zone(pgdat->node_zones + z)) break; } wakeup_kswapd(pgdat->node_zones + z, 0, order, ZONE_MOVABLE); return 0; } if (isolate_lru_page(page)) return 0; mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON + page_is_file_lru(page), nr_pages); /* * Isolating the page has taken another reference, so the * caller's reference can be safely dropped without the page * disappearing underneath us during migration. */ put_page(page); return 1; } /* * Attempt to migrate a misplaced page to the specified destination * node. Caller is expected to have an elevated reference count on * the page that will be dropped by this function before returning. */ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma, int node) { pg_data_t *pgdat = NODE_DATA(node); int isolated; int nr_remaining; unsigned int nr_succeeded; LIST_HEAD(migratepages); int nr_pages = thp_nr_pages(page); /* * Don't migrate file pages that are mapped in multiple processes * with execute permissions as they are probably shared libraries. */ if (page_mapcount(page) != 1 && page_is_file_lru(page) && (vma->vm_flags & VM_EXEC)) goto out; /* * Also do not migrate dirty pages as not all filesystems can move * dirty pages in MIGRATE_ASYNC mode which is a waste of cycles. */ if (page_is_file_lru(page) && PageDirty(page)) goto out; isolated = numamigrate_isolate_page(pgdat, page); if (!isolated) goto out; list_add(&page->lru, &migratepages); nr_remaining = migrate_pages(&migratepages, alloc_misplaced_dst_page, NULL, node, MIGRATE_ASYNC, MR_NUMA_MISPLACED, &nr_succeeded); if (nr_remaining) { if (!list_empty(&migratepages)) { list_del(&page->lru); mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON + page_is_file_lru(page), -nr_pages); putback_lru_page(page); } isolated = 0; } if (nr_succeeded) { count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_succeeded); if (!node_is_toptier(page_to_nid(page)) && node_is_toptier(node)) mod_node_page_state(pgdat, PGPROMOTE_SUCCESS, nr_succeeded); } BUG_ON(!list_empty(&migratepages)); return isolated; out: put_page(page); return 0; } #endif /* CONFIG_NUMA_BALANCING */ /* * node_demotion[] example: * * Consider a system with two sockets. Each socket has * three classes of memory attached: fast, medium and slow. * Each memory class is placed in its own NUMA node. The * CPUs are placed in the node with the "fast" memory. The * 6 NUMA nodes (0-5) might be split among the sockets like * this: * * Socket A: 0, 1, 2 * Socket B: 3, 4, 5 * * When Node 0 fills up, its memory should be migrated to * Node 1. When Node 1 fills up, it should be migrated to * Node 2. The migration path start on the nodes with the * processors (since allocations default to this node) and * fast memory, progress through medium and end with the * slow memory: * * 0 -> 1 -> 2 -> stop * 3 -> 4 -> 5 -> stop * * This is represented in the node_demotion[] like this: * * { nr=1, nodes[0]=1 }, // Node 0 migrates to 1 * { nr=1, nodes[0]=2 }, // Node 1 migrates to 2 * { nr=0, nodes[0]=-1 }, // Node 2 does not migrate * { nr=1, nodes[0]=4 }, // Node 3 migrates to 4 * { nr=1, nodes[0]=5 }, // Node 4 migrates to 5 * { nr=0, nodes[0]=-1 }, // Node 5 does not migrate * * Moreover some systems may have multiple slow memory nodes. * Suppose a system has one socket with 3 memory nodes, node 0 * is fast memory type, and node 1/2 both are slow memory * type, and the distance between fast memory node and slow * memory node is same. So the migration path should be: * * 0 -> 1/2 -> stop * * This is represented in the node_demotion[] like this: * { nr=2, {nodes[0]=1, nodes[1]=2} }, // Node 0 migrates to node 1 and node 2 * { nr=0, nodes[0]=-1, }, // Node 1 dose not migrate * { nr=0, nodes[0]=-1, }, // Node 2 does not migrate */ /* * Writes to this array occur without locking. Cycles are * not allowed: Node X demotes to Y which demotes to X... * * If multiple reads are performed, a single rcu_read_lock() * must be held over all reads to ensure that no cycles are * observed. */ #define DEFAULT_DEMOTION_TARGET_NODES 15 #if MAX_NUMNODES < DEFAULT_DEMOTION_TARGET_NODES #define DEMOTION_TARGET_NODES (MAX_NUMNODES - 1) #else #define DEMOTION_TARGET_NODES DEFAULT_DEMOTION_TARGET_NODES #endif struct demotion_nodes { unsigned short nr; short nodes[DEMOTION_TARGET_NODES]; }; static struct demotion_nodes *node_demotion __read_mostly; /** * next_demotion_node() - Get the next node in the demotion path * @node: The starting node to lookup the next node * * Return: node id for next memory node in the demotion path hierarchy * from @node; NUMA_NO_NODE if @node is terminal. This does not keep * @node online or guarantee that it *continues* to be the next demotion * target. */ int next_demotion_node(int node) { struct demotion_nodes *nd; unsigned short target_nr, index; int target; if (!node_demotion) return NUMA_NO_NODE; nd = &node_demotion[node]; /* * node_demotion[] is updated without excluding this * function from running. RCU doesn't provide any * compiler barriers, so the READ_ONCE() is required * to avoid compiler reordering or read merging. * * Make sure to use RCU over entire code blocks if * node_demotion[] reads need to be consistent. */ rcu_read_lock(); target_nr = READ_ONCE(nd->nr); switch (target_nr) { case 0: target = NUMA_NO_NODE; goto out; case 1: index = 0; break; default: /* * If there are multiple target nodes, just select one * target node randomly. * * In addition, we can also use round-robin to select * target node, but we should introduce another variable * for node_demotion[] to record last selected target node, * that may cause cache ping-pong due to the changing of * last target node. Or introducing per-cpu data to avoid * caching issue, which seems more complicated. So selecting * target node randomly seems better until now. */ index = get_random_int() % target_nr; break; } target = READ_ONCE(nd->nodes[index]); out: rcu_read_unlock(); return target; } /* Disable reclaim-based migration. */ static void __disable_all_migrate_targets(void) { int node, i; if (!node_demotion) return; for_each_online_node(node) { node_demotion[node].nr = 0; for (i = 0; i < DEMOTION_TARGET_NODES; i++) node_demotion[node].nodes[i] = NUMA_NO_NODE; } } static void disable_all_migrate_targets(void) { __disable_all_migrate_targets(); /* * Ensure that the "disable" is visible across the system. * Readers will see either a combination of before+disable * state or disable+after. They will never see before and * after state together. * * The before+after state together might have cycles and * could cause readers to do things like loop until this * function finishes. This ensures they can only see a * single "bad" read and would, for instance, only loop * once. */ synchronize_rcu(); } /* * Find an automatic demotion target for 'node'. * Failing here is OK. It might just indicate * being at the end of a chain. */ static int establish_migrate_target(int node, nodemask_t *used, int best_distance) { int migration_target, index, val; struct demotion_nodes *nd; if (!node_demotion) return NUMA_NO_NODE; nd = &node_demotion[node]; migration_target = find_next_best_node(node, used); if (migration_target == NUMA_NO_NODE) return NUMA_NO_NODE; /* * If the node has been set a migration target node before, * which means it's the best distance between them. Still * check if this node can be demoted to other target nodes * if they have a same best distance. */ if (best_distance != -1) { val = node_distance(node, migration_target); if (val > best_distance) goto out_clear; } index = nd->nr; if (WARN_ONCE(index >= DEMOTION_TARGET_NODES, "Exceeds maximum demotion target nodes\n")) goto out_clear; nd->nodes[index] = migration_target; nd->nr++; return migration_target; out_clear: node_clear(migration_target, *used); return NUMA_NO_NODE; } /* * When memory fills up on a node, memory contents can be * automatically migrated to another node instead of * discarded at reclaim. * * Establish a "migration path" which will start at nodes * with CPUs and will follow the priorities used to build the * page allocator zonelists. * * The difference here is that cycles must be avoided. If * node0 migrates to node1, then neither node1, nor anything * node1 migrates to can migrate to node0. Also one node can * be migrated to multiple nodes if the target nodes all have * a same best-distance against the source node. * * This function can run simultaneously with readers of * node_demotion[]. However, it can not run simultaneously * with itself. Exclusion is provided by memory hotplug events * being single-threaded. */ static void __set_migration_target_nodes(void) { nodemask_t next_pass; nodemask_t this_pass; nodemask_t used_targets = NODE_MASK_NONE; int node, best_distance; /* * Avoid any oddities like cycles that could occur * from changes in the topology. This will leave * a momentary gap when migration is disabled. */ disable_all_migrate_targets(); /* * Allocations go close to CPUs, first. Assume that * the migration path starts at the nodes with CPUs. */ next_pass = node_states[N_CPU]; again: this_pass = next_pass; next_pass = NODE_MASK_NONE; /* * To avoid cycles in the migration "graph", ensure * that migration sources are not future targets by * setting them in 'used_targets'. Do this only * once per pass so that multiple source nodes can * share a target node. * * 'used_targets' will become unavailable in future * passes. This limits some opportunities for * multiple source nodes to share a destination. */ nodes_or(used_targets, used_targets, this_pass); for_each_node_mask(node, this_pass) { best_distance = -1; /* * Try to set up the migration path for the node, and the target * migration nodes can be multiple, so doing a loop to find all * the target nodes if they all have a best node distance. */ do { int target_node = establish_migrate_target(node, &used_targets, best_distance); if (target_node == NUMA_NO_NODE) break; if (best_distance == -1) best_distance = node_distance(node, target_node); /* * Visit targets from this pass in the next pass. * Eventually, every node will have been part of * a pass, and will become set in 'used_targets'. */ node_set(target_node, next_pass); } while (1); } /* * 'next_pass' contains nodes which became migration * targets in this pass. Make additional passes until * no more migrations targets are available. */ if (!nodes_empty(next_pass)) goto again; } /* * For callers that do not hold get_online_mems() already. */ void set_migration_target_nodes(void) { get_online_mems(); __set_migration_target_nodes(); put_online_mems(); } /* * This leaves migrate-on-reclaim transiently disabled between * the MEM_GOING_OFFLINE and MEM_OFFLINE events. This runs * whether reclaim-based migration is enabled or not, which * ensures that the user can turn reclaim-based migration at * any time without needing to recalculate migration targets. * * These callbacks already hold get_online_mems(). That is why * __set_migration_target_nodes() can be used as opposed to * set_migration_target_nodes(). */ #ifdef CONFIG_MEMORY_HOTPLUG static int __meminit migrate_on_reclaim_callback(struct notifier_block *self, unsigned long action, void *_arg) { struct memory_notify *arg = _arg; /* * Only update the node migration order when a node is * changing status, like online->offline. This avoids * the overhead of synchronize_rcu() in most cases. */ if (arg->status_change_nid < 0) return notifier_from_errno(0); switch (action) { case MEM_GOING_OFFLINE: /* * Make sure there are not transient states where * an offline node is a migration target. This * will leave migration disabled until the offline * completes and the MEM_OFFLINE case below runs. */ disable_all_migrate_targets(); break; case MEM_OFFLINE: case MEM_ONLINE: /* * Recalculate the target nodes once the node * reaches its final state (online or offline). */ __set_migration_target_nodes(); break; case MEM_CANCEL_OFFLINE: /* * MEM_GOING_OFFLINE disabled all the migration * targets. Reenable them. */ __set_migration_target_nodes(); break; case MEM_GOING_ONLINE: case MEM_CANCEL_ONLINE: break; } return notifier_from_errno(0); } #endif void __init migrate_on_reclaim_init(void) { node_demotion = kcalloc(nr_node_ids, sizeof(struct demotion_nodes), GFP_KERNEL); WARN_ON(!node_demotion); #ifdef CONFIG_MEMORY_HOTPLUG hotplug_memory_notifier(migrate_on_reclaim_callback, 100); #endif /* * At this point, all numa nodes with memory/CPus have their state * properly set, so we can build the demotion order now. * Let us hold the cpu_hotplug lock just, as we could possibily have * CPU hotplug events during boot. */ cpus_read_lock(); set_migration_target_nodes(); cpus_read_unlock(); } bool numa_demotion_enabled = false; #ifdef CONFIG_SYSFS static ssize_t numa_demotion_enabled_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { return sysfs_emit(buf, "%s\n", numa_demotion_enabled ? "true" : "false"); } static ssize_t numa_demotion_enabled_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count) { if (!strncmp(buf, "true", 4) || !strncmp(buf, "1", 1)) numa_demotion_enabled = true; else if (!strncmp(buf, "false", 5) || !strncmp(buf, "0", 1)) numa_demotion_enabled = false; else return -EINVAL; return count; } static struct kobj_attribute numa_demotion_enabled_attr = __ATTR(demotion_enabled, 0644, numa_demotion_enabled_show, numa_demotion_enabled_store); static struct attribute *numa_attrs[] = { &numa_demotion_enabled_attr.attr, NULL, }; static const struct attribute_group numa_attr_group = { .attrs = numa_attrs, }; static int __init numa_init_sysfs(void) { int err; struct kobject *numa_kobj; numa_kobj = kobject_create_and_add("numa", mm_kobj); if (!numa_kobj) { pr_err("failed to create numa kobject\n"); return -ENOMEM; } err = sysfs_create_group(numa_kobj, &numa_attr_group); if (err) { pr_err("failed to register numa group\n"); goto delete_obj; } return 0; delete_obj: kobject_put(numa_kobj); return err; } subsys_initcall(numa_init_sysfs); #endif /* CONFIG_SYSFS */ #endif /* CONFIG_NUMA */