From 7aad25b4b47ea5b67e1eb8be0db211b899dce60d Mon Sep 17 00:00:00 2001 From: Kairui Song Date: Wed, 22 May 2024 01:58:53 +0800 Subject: [PATCH] mm/swap: reduce swap cache search space Currently we use one swap_address_space for every 64M chunk to reduce lock contention, this is like having a set of smaller swap files inside one swap device. But when doing swap cache look up or insert, we are still using the offset of the whole large swap device. This is OK for correctness, as the offset (key) is unique. But Xarray is specially optimized for small indexes, it creates the radix tree levels lazily to be just enough to fit the largest key stored in one Xarray. So we are wasting tree nodes unnecessarily. For 64M chunk it should only take at most 3 levels to contain everything. But if we are using the offset from the whole swap device, the offset (key) value will be way beyond 64M, and so will the tree level. Optimize this by using a new helper swap_cache_index to get a swap entry's unique offset in its own 64M swap_address_space. I see a ~1% performance gain in benchmark and actual workload with high memory pressure. Test with `time memhog 128G` inside a 8G memcg using 128G swap (ramdisk with SWP_SYNCHRONOUS_IO dropped, tested 3 times, results are stable. The test result is similar but the improvement is smaller if SWP_SYNCHRONOUS_IO is enabled, as swap out path can never skip swap cache): Before: 6.07user 250.74system 4:17.26elapsed 99%CPU (0avgtext+0avgdata 8373376maxresident)k 0inputs+0outputs (55major+33555018minor)pagefaults 0swaps After (1.8% faster): 6.08user 246.09system 4:12.58elapsed 99%CPU (0avgtext+0avgdata 8373248maxresident)k 0inputs+0outputs (54major+33555027minor)pagefaults 0swaps Similar result with MySQL and sysbench using swap: Before: 94055.61 qps After (0.8% faster): 94834.91 qps Radix tree slab usage is also very slightly lower. Link: https://lkml.kernel.org/r/20240521175854.96038-12-ryncsn@gmail.com Signed-off-by: Kairui Song Reviewed-by: "Huang, Ying" Cc: Anna Schumaker Cc: Barry Song Cc: Chao Yu Cc: Chris Li Cc: David Hildenbrand Cc: David Howells Cc: Hugh Dickins Cc: Ilya Dryomov Cc: Jaegeuk Kim Cc: Jeff Layton Cc: Marc Dionne Cc: Matthew Wilcox (Oracle) Cc: Minchan Kim Cc: NeilBrown Cc: Ryan Roberts Cc: Ryusuke Konishi Cc: Trond Myklebust Cc: Xiubo Li Cc: Yosry Ahmed Signed-off-by: Andrew Morton --- mm/huge_memory.c | 2 +- mm/memcontrol.c | 2 +- mm/mincore.c | 2 +- mm/shmem.c | 2 +- mm/swap.h | 15 +++++++++++++++ mm/swap_state.c | 17 +++++++++-------- mm/swapfile.c | 6 +++--- 7 files changed, 31 insertions(+), 15 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index db7946a0a28c..cff47b3fc72e 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2838,7 +2838,7 @@ static void __split_huge_page(struct page *page, struct list_head *list, split_page_memcg(head, order, new_order); if (folio_test_anon(folio) && folio_test_swapcache(folio)) { - offset = swp_offset(folio->swap); + offset = swap_cache_index(folio->swap); swap_cache = swap_address_space(folio->swap); xa_lock(&swap_cache->i_pages); } diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 71fe2a95b8bd..86a741d8a37d 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -6146,7 +6146,7 @@ static struct page *mc_handle_swap_pte(struct vm_area_struct *vma, * Because swap_cache_get_folio() updates some statistics counter, * we call find_get_page() with swapper_space directly. */ - page = find_get_page(swap_address_space(ent), swp_offset(ent)); + page = find_get_page(swap_address_space(ent), swap_cache_index(ent)); entry->val = ent.val; return page; diff --git a/mm/mincore.c b/mm/mincore.c index dad3622cc963..e31cf1bde614 100644 --- a/mm/mincore.c +++ b/mm/mincore.c @@ -139,7 +139,7 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, } else { #ifdef CONFIG_SWAP *vec = mincore_page(swap_address_space(entry), - swp_offset(entry)); + swap_cache_index(entry)); #else WARN_ON(1); *vec = 1; diff --git a/mm/shmem.c b/mm/shmem.c index b2dce4103f0e..3e7d60d71d31 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1742,7 +1742,7 @@ static int shmem_replace_folio(struct folio **foliop, gfp_t gfp, old = *foliop; entry = old->swap; - swap_index = swp_offset(entry); + swap_index = swap_cache_index(entry); swap_mapping = swap_address_space(entry); /* diff --git a/mm/swap.h b/mm/swap.h index 82023ab93205..2c0e96272d49 100644 --- a/mm/swap.h +++ b/mm/swap.h @@ -27,6 +27,7 @@ void __swap_writepage(struct folio *folio, struct writeback_control *wbc); /* One swap address space for each 64M swap space */ #define SWAP_ADDRESS_SPACE_SHIFT 14 #define SWAP_ADDRESS_SPACE_PAGES (1 << SWAP_ADDRESS_SPACE_SHIFT) +#define SWAP_ADDRESS_SPACE_MASK (SWAP_ADDRESS_SPACE_PAGES - 1) extern struct address_space *swapper_spaces[]; #define swap_address_space(entry) \ (&swapper_spaces[swp_type(entry)][swp_offset(entry) \ @@ -40,6 +41,15 @@ static inline loff_t swap_dev_pos(swp_entry_t entry) return ((loff_t)swp_offset(entry)) << PAGE_SHIFT; } +/* + * Return the swap cache index of the swap entry. + */ +static inline pgoff_t swap_cache_index(swp_entry_t entry) +{ + BUILD_BUG_ON((SWP_OFFSET_MASK | SWAP_ADDRESS_SPACE_MASK) != SWP_OFFSET_MASK); + return swp_offset(entry) & SWAP_ADDRESS_SPACE_MASK; +} + void show_swap_cache_info(void); bool add_to_swap(struct folio *folio); void *get_shadow_from_swap_cache(swp_entry_t entry); @@ -86,6 +96,11 @@ static inline struct address_space *swap_address_space(swp_entry_t entry) return NULL; } +static inline pgoff_t swap_cache_index(swp_entry_t entry) +{ + return 0; +} + static inline void show_swap_cache_info(void) { } diff --git a/mm/swap_state.c b/mm/swap_state.c index 6498491e3ad8..a5dae40523ab 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -72,7 +72,7 @@ void show_swap_cache_info(void) void *get_shadow_from_swap_cache(swp_entry_t entry) { struct address_space *address_space = swap_address_space(entry); - pgoff_t idx = swp_offset(entry); + pgoff_t idx = swap_cache_index(entry); void *shadow; shadow = xa_load(&address_space->i_pages, idx); @@ -89,7 +89,7 @@ int add_to_swap_cache(struct folio *folio, swp_entry_t entry, gfp_t gfp, void **shadowp) { struct address_space *address_space = swap_address_space(entry); - pgoff_t idx = swp_offset(entry); + pgoff_t idx = swap_cache_index(entry); XA_STATE_ORDER(xas, &address_space->i_pages, idx, folio_order(folio)); unsigned long i, nr = folio_nr_pages(folio); void *old; @@ -144,7 +144,7 @@ void __delete_from_swap_cache(struct folio *folio, struct address_space *address_space = swap_address_space(entry); int i; long nr = folio_nr_pages(folio); - pgoff_t idx = swp_offset(entry); + pgoff_t idx = swap_cache_index(entry); XA_STATE(xas, &address_space->i_pages, idx); xas_set_update(&xas, workingset_update_node); @@ -253,13 +253,14 @@ void clear_shadow_from_swap_cache(int type, unsigned long begin, for (;;) { swp_entry_t entry = swp_entry(type, curr); + unsigned long index = curr & SWAP_ADDRESS_SPACE_MASK; struct address_space *address_space = swap_address_space(entry); - XA_STATE(xas, &address_space->i_pages, curr); + XA_STATE(xas, &address_space->i_pages, index); xas_set_update(&xas, workingset_update_node); xa_lock_irq(&address_space->i_pages); - xas_for_each(&xas, old, end) { + xas_for_each(&xas, old, min(index + (end - curr), SWAP_ADDRESS_SPACE_PAGES)) { if (!xa_is_value(old)) continue; xas_store(&xas, NULL); @@ -350,7 +351,7 @@ struct folio *swap_cache_get_folio(swp_entry_t entry, { struct folio *folio; - folio = filemap_get_folio(swap_address_space(entry), swp_offset(entry)); + folio = filemap_get_folio(swap_address_space(entry), swap_cache_index(entry)); if (!IS_ERR(folio)) { bool vma_ra = swap_use_vma_readahead(); bool readahead; @@ -420,7 +421,7 @@ struct folio *filemap_get_incore_folio(struct address_space *mapping, si = get_swap_device(swp); if (!si) return ERR_PTR(-ENOENT); - index = swp_offset(swp); + index = swap_cache_index(swp); folio = filemap_get_folio(swap_address_space(swp), index); put_swap_device(si); return folio; @@ -447,7 +448,7 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, * that would confuse statistics. */ folio = filemap_get_folio(swap_address_space(entry), - swp_offset(entry)); + swap_cache_index(entry)); if (!IS_ERR(folio)) goto got_folio; diff --git a/mm/swapfile.c b/mm/swapfile.c index 348c4d3ae078..f1e559e216bd 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -142,7 +142,7 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si, struct folio *folio; int ret = 0; - folio = filemap_get_folio(swap_address_space(entry), offset); + folio = filemap_get_folio(swap_address_space(entry), swap_cache_index(entry)); if (IS_ERR(folio)) return 0; /* @@ -2158,7 +2158,7 @@ retry: (i = find_next_to_unuse(si, i)) != 0) { entry = swp_entry(type, i); - folio = filemap_get_folio(swap_address_space(entry), i); + folio = filemap_get_folio(swap_address_space(entry), swap_cache_index(entry)); if (IS_ERR(folio)) continue; @@ -3451,7 +3451,7 @@ EXPORT_SYMBOL_GPL(swapcache_mapping); pgoff_t __folio_swap_cache_index(struct folio *folio) { - return swp_offset(folio->swap); + return swap_cache_index(folio->swap); } EXPORT_SYMBOL_GPL(__folio_swap_cache_index);