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linux/mm
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Linus Torvalds 1b2de5d039 mm/cow: don't bother write protecting already write-protected pages 
This is not normally noticeable, but repeated forks are unnecessarily
expensive because they repeatedly dirty the parent page tables during
the page table copy operation.

It's trivial to just avoid write protecting the page table entry if it
was already not writable.

This patch was inspired by

    https://bugzilla.kernel.org/show_bug.cgi?id=200447

which points to an ancient "waste time re-doing fork" issue in the
presence of lots of signals.

That bug was fixed by Eric Biederman's signal handling series
culminating in commit c3ad2c3b02 ("signal: Don't restart fork when
signals come in"), but the unnecessary work for repeated forks is still
work just fixing, particularly since the fix is trivial.

Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-08-25 13:15:03 -07:00
..
kasan kernel/memremap, kasan: make ZONE_DEVICE with work with KASAN 2018-08-17 16:20:30 -07:00
backing-dev.c bdi: use irqsave variant of refcount_dec_and_lock() 2018-08-22 10:52:46 -07:00
balloon_compaction.c
bootmem.c docs/mm: bootmem: add overview documentation 2018-08-02 12:17:27 -06:00
cleancache.c mm: use octal not symbolic permissions 2018-06-15 07:55:25 +09:00
cma_debug.c mm/cma: remove unsupported gfp_mask parameter from cma_alloc() 2018-08-17 16:20:32 -07:00
cma.c mm/cma: remove unsupported gfp_mask parameter from cma_alloc() 2018-08-17 16:20:32 -07:00
cma.h
compaction.c mm: use octal not symbolic permissions 2018-06-15 07:55:25 +09:00
debug_page_ref.c
debug.c mm: teach dump_page() to correctly output poisoned struct pages 2018-07-03 17:32:19 -07:00
dmapool.c mm: use octal not symbolic permissions 2018-06-15 07:55:25 +09:00
early_ioremap.c
fadvise.c mm/fadvise.c: fix signed overflow UBSAN complaint 2018-08-17 16:20:30 -07:00
failslab.c mm: use octal not symbolic permissions 2018-06-15 07:55:25 +09:00
filemap.c mm: use new return type vm_fault_t 2018-06-07 17:34:36 -07:00
frame_vector.c
frontswap.c mm: use octal not symbolic permissions 2018-06-15 07:55:25 +09:00
gup_benchmark.c treewide: kvzalloc() -> kvcalloc() 2018-06-12 16:19:22 -07:00
gup.c mm: Change return type int to vm_fault_t for fault handlers 2018-08-23 18:48:44 -07:00
highmem.c
hmm.c mm, oom: distinguish blockable mode for mmu notifiers 2018-08-22 10:52:44 -07:00
huge_memory.c mm: Change return type int to vm_fault_t for fault handlers 2018-08-23 18:48:44 -07:00
hugetlb_cgroup.c mm: rename page_counter's count/limit into usage/max 2018-06-07 17:34:35 -07:00
hugetlb.c mm: Change return type int to vm_fault_t for fault handlers 2018-08-23 18:48:44 -07:00
hwpoison-inject.c
init-mm.c mm: Allocate the mm_cpumask (mm->cpu_bitmap[]) dynamically based on nr_cpu_ids 2018-07-17 09:35:30 +02:00
internal.h mm: Change return type int to vm_fault_t for fault handlers 2018-08-23 18:48:44 -07:00
interval_tree.c
Kconfig mm, swap: make CONFIG_THP_SWAP depend on CONFIG_SWAP 2018-08-17 16:20:32 -07:00
Kconfig.debug mm: clarify CONFIG_PAGE_POISONING and usage 2018-08-22 10:52:44 -07:00
khugepaged.c mm: Change return type int to vm_fault_t for fault handlers 2018-08-23 18:48:44 -07:00
kmemleak-test.c
kmemleak.c
ksm.c include/linux/compiler*.h: make compiler-*.h mutually exclusive 2018-08-22 17:31:34 -07:00
list_lru.c mm/list_lru: introduce list_lru_shrink_walk_irq() 2018-08-17 16:20:32 -07:00
maccess.c
madvise.c
Makefile mm: restructure memfd code 2018-06-07 17:34:35 -07:00
memblock.c mm/memblock.c: replace u64 with phys_addr_t where appropriate 2018-08-17 16:20:30 -07:00
memcontrol.c mm, oom: introduce memory.oom.group 2018-08-22 10:52:45 -07:00
memfd.c alloc_file(): switch to passing O_... flags instead of FMODE_... mode 2018-07-12 10:02:57 -04:00
memory_hotplug.c mm/page_alloc: Introduce free_area_init_core_hotplug 2018-08-22 10:52:45 -07:00
memory-failure.c mm: soft-offline: close the race against page allocation 2018-08-23 18:48:43 -07:00
memory.c mm/cow: don't bother write protecting already write-protected pages 2018-08-25 13:15:03 -07:00
mempolicy.c mm: access zone->node via zone_to_nid() and zone_set_nid() 2018-08-22 10:52:45 -07:00
mempool.c mm/mempool.c: add missing parameter description 2018-08-22 10:52:44 -07:00
memtest.c
migrate.c mm: soft-offline: close the race against page allocation 2018-08-23 18:48:43 -07:00
mincore.c
mlock.c dax: remove VM_MIXEDMAP for fsdax and device dax 2018-08-17 16:20:27 -07:00
mm_init.c mm: access zone->node via zone_to_nid() and zone_set_nid() 2018-08-22 10:52:45 -07:00
mmap.c mm, oom: remove oom_lock from oom_reaper 2018-08-22 10:52:44 -07:00
mmu_context.c
mmu_notifier.c mm, oom: distinguish blockable mode for mmu notifiers 2018-08-22 10:52:44 -07:00
mmzone.c
mprotect.c x86/speculation/l1tf: Disallow non privileged high MMIO PROT_NONE mappings 2018-06-20 19:10:01 +02:00
mremap.c mremap: remove LATENCY_LIMIT from mremap to reduce the number of TLB shootdowns 2018-06-15 07:55:24 +09:00
msync.c
nobootmem.c mm/memblock: add a name for memblock flags enumeration 2018-08-02 12:17:27 -06:00
nommu.c mm: provide a fallback for PAGE_KERNEL_EXEC for architectures 2018-08-17 16:20:29 -07:00
oom_kill.c Merge branch 'akpm' (patches from Andrew) 2018-08-22 12:34:08 -07:00
page_alloc.c mm: soft-offline: close the race against page allocation 2018-08-23 18:48:43 -07:00
page_counter.c memcg: introduce memory.min 2018-06-07 17:34:36 -07:00
page_ext.c mm/page_ext.c: constify lookup_page_ext() argument 2018-08-17 16:20:28 -07:00
page_idle.c mm: use octal not symbolic permissions 2018-06-15 07:55:25 +09:00
page_io.c swap,blkcg: issue swap io with the appropriate context 2018-07-09 09:07:54 -06:00
page_isolation.c mm, migrate: remove reason argument from new_page_t 2018-04-11 10:28:32 -07:00
page_owner.c mm: use octal not symbolic permissions 2018-06-15 07:55:25 +09:00
page_poison.c
page_vma_mapped.c
page-writeback.c mm/page-writeback.c: update stale account_page_redirty() comment 2018-08-17 16:20:30 -07:00
pagewalk.c
percpu-internal.h
percpu-km.c
percpu-stats.c treewide: Use array_size() in vmalloc() 2018-06-12 16:19:22 -07:00
percpu-vm.c
percpu.c /proc/meminfo: add percpu populated pages count 2018-08-22 10:52:45 -07:00
pgtable-generic.c
process_vm_access.c
quicklist.c
readahead.c readahead: stricter check for bdi io_pages 2018-07-27 09:09:53 -06:00
rmap.c mm: do not drop unused pages when userfaultd is running 2018-07-14 11:11:09 -07:00
rodata_test.c
shmem.c mm: Change return type int to vm_fault_t for fault handlers 2018-08-23 18:48:44 -07:00
slab_common.c mm: introduce CONFIG_MEMCG_KMEM as combination of CONFIG_MEMCG && !CONFIG_SLOB 2018-08-17 16:20:30 -07:00
slab.c treewide: kzalloc() -> kcalloc() 2018-06-12 16:19:22 -07:00
slab.h mm: introduce CONFIG_MEMCG_KMEM as combination of CONFIG_MEMCG && !CONFIG_SLOB 2018-08-17 16:20:30 -07:00
slob.c slab: __GFP_ZERO is incompatible with a constructor 2018-06-07 17:34:34 -07:00
slub.c mm, slub: restore the original intention of prefetch_freepointer() 2018-08-17 16:20:28 -07:00
sparse-vmemmap.c mm/sparse: delete old sparse_init and enable new one 2018-08-17 16:20:32 -07:00
sparse.c mm/sparse: delete old sparse_init and enable new one 2018-08-17 16:20:32 -07:00
swap_cgroup.c
swap_slots.c mm, swap, get_swap_pages: use entry_size instead of cluster in parameter 2018-08-22 10:52:44 -07:00
swap_state.c treewide: kvzalloc() -> kvcalloc() 2018-06-12 16:19:22 -07:00
swap.c mm: introduce MEMORY_DEVICE_FS_DAX and CONFIG_DEV_PAGEMAP_OPS 2018-05-22 06:59:39 -07:00
swapfile.c mm/swapfile.c: put_swap_page: share more between huge/normal code path 2018-08-22 10:52:44 -07:00
truncate.c page cache: use xa_lock 2018-04-11 10:28:39 -07:00
usercopy.c usercopy: Allow boot cmdline disabling of hardening 2018-07-04 08:04:52 -07:00
userfaultfd.c userfaultfd: prevent non-cooperative events vs mcopy_atomic races 2018-06-07 17:34:38 -07:00
util.c mm/util: add kernel-doc for kvfree 2018-08-23 18:48:43 -07:00
vmacache.c mm, vmacache: hash addresses based on pmd 2018-08-17 16:20:32 -07:00
vmalloc.c mm: provide a fallback for PAGE_KERNEL_EXEC for architectures 2018-08-17 16:20:29 -07:00
vmpressure.c mm/vmpressure.c: convert to use match_string() helper 2018-06-07 17:34:36 -07:00
vmscan.c mm: fix page_freeze_refs and page_unfreeze_refs in comments 2018-08-22 10:52:44 -07:00
vmstat.c Revert mm/vmstat.c: fix vmstat_update() preemption BUG 2018-06-28 11:16:44 -07:00
workingset.c mm/list_lru: introduce list_lru_shrink_walk_irq() 2018-08-17 16:20:32 -07:00
z3fold.c z3fold: fix reclaim lock-ups 2018-05-11 17:28:45 -07:00
zbud.c
zpool.c
zsmalloc.c mm/zsmalloc.c: make several functions and a struct static 2018-08-17 16:20:30 -07:00
zswap.c zswap: re-check zswap_is_full() after do zswap_shrink() 2018-07-26 19:38:03 -07:00