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9b91432985
linux/mm
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Lorenzo Stoakes 9b91432985 mm/mprotect: allow unfaulted VMAs to be unaccounted on mprotect() 
When mprotect() is used to make unwritable VMAs writable, they have the
VM_ACCOUNT flag applied and memory accounted accordingly.

If the VMA has had no pages faulted in and is then made unwritable once
again, it will remain accounted for, despite not being capable of
extending memory usage.

Consider:-

ptr = mmap(NULL, page_size * 3, PROT_READ, MAP_ANON | MAP_PRIVATE, -1, 0);
mprotect(ptr + page_size, page_size, PROT_READ | PROT_WRITE);
mprotect(ptr + page_size, page_size, PROT_READ);

The first mprotect() splits the range into 3 VMAs and the second fails to
merge the three as the middle VMA has VM_ACCOUNT set and the others do
not, rendering them unmergeable.

This is unnecessary, since no pages have actually been allocated and the
middle VMA is not capable of utilising more memory, thereby introducing
unnecessary VMA fragmentation (and accounting for more memory than is
necessary).

Since we cannot efficiently determine which pages map to an anonymous VMA,
we have to be very conservative - determining whether any pages at all
have been faulted in, by checking whether vma->anon_vma is NULL.

We can see that the lack of anon_vma implies that no anonymous pages are
present as evidenced by vma_needs_copy() utilising this on fork to
determine whether page tables need to be copied.

The only place where anon_vma is set NULL explicitly is on fork with
VM_WIPEONFORK set, however since this flag is intended to cause the child
process to not CoW on a given memory range, it is right to interpret this
as indicating the VMA has no faulted-in anonymous memory mapped.

If the VMA was forked without VM_WIPEONFORK set, then anon_vma_fork() will
have ensured that a new anon_vma is assigned (and correctly related to its
parent anon_vma) should any pages be CoW-mapped.

The overall operation is safe against races as we hold a write lock against
mm->mmap_lock.

If we could efficiently look up the VMA's faulted-in pages then we would
unaccount all those pages not yet faulted in.  However as the original
comment alludes this simply isn't currently possible, so we are
conservative and account all pages or none at all.

Link: https://lkml.kernel.org/r/ad5540371a16623a069f03f4db1739f33cde1fab.1696921767.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-10-18 14:34:18 -07:00
..
damon Merge mm-hotfixes-stable into mm-stable to pick up depended-upon changes. 2023-10-18 14:32:58 -07:00
kasan mm: delete checks for xor_unlock_is_negative_byte() 2023-10-18 14:34:17 -07:00
kfence LoongArch changes for v6.6 2023-09-08 12:16:52 -07:00
kmsan kmsan: introduce test_memcpy_initialized_gap() 2023-10-04 10:32:22 -07:00
backing-dev.c writeback: remove redundant checks for root memcg 2023-08-21 13:37:48 -07:00
balloon_compaction.c
bootmem_info.c
cma_debug.c
cma_sysfs.c mm: cma: make kobj_type structure constant 2023-03-28 16:20:06 -07:00
cma.c mm/cma: use nth_page() in place of direct struct page manipulation 2023-10-04 10:32:29 -07:00
cma.h
compaction.c mm/compaction: factor out code to test if we should run compaction for target order 2023-10-04 10:32:19 -07:00
debug_page_alloc.c mm: page_alloc: split out DEBUG_PAGEALLOC 2023-06-09 16:25:23 -07:00
debug_page_ref.c
debug_vm_pgtable.c Add x86 shadow stack support 2023-08-31 12:20:12 -07:00
debug.c mm: update validate_mm() to use vma iterator 2023-06-09 16:25:31 -07:00
dmapool_test.c dmapool: add alloc/free performance test 2023-04-05 19:42:38 -07:00
dmapool.c dmapool: create/destroy cleanup 2023-06-09 16:25:17 -07:00
early_ioremap.c mm/early_ioremap.c: improve the execution efficiency of early_ioremap_setup() 2023-06-09 16:25:56 -07:00
fadvise.c mm: remove unnecessary pagevec includes 2023-06-23 16:59:31 -07:00
fail_page_alloc.c mm: page_alloc: split out FAIL_PAGE_ALLOC 2023-06-09 16:25:23 -07:00
failslab.c
filemap.c memcontrol: only transfer the memcg data for migration 2023-10-18 14:34:17 -07:00
folio-compat.c filemap: Add fgf_t typedef 2023-07-24 18:04:30 -04:00
gup_test.c Merge mm-hotfixes-stable into mm-stable to pick up depended-upon changes. 2023-06-23 16:58:19 -07:00
gup_test.h
gup.c mm/gup: make failure to pin an error if FOLL_NOWAIT not specified 2023-10-18 14:34:15 -07:00
highmem.c mm: ptep_get() conversion 2023-06-19 16:19:25 -07:00
hmm.c mm: enable page walking API to lock vmas during the walk 2023-08-21 13:07:20 -07:00
huge_memory.c mm/thp: fix "mm: thp: kill __transhuge_page_enabled()" 2023-10-18 14:34:18 -07:00
hugetlb_cgroup.c mm, hugetlb: remove HUGETLB_CGROUP_MIN_ORDER 2023-10-18 14:34:17 -07:00
hugetlb_vmemmap.c mm: hugetlb: skip initialization of gigantic tail struct pages if freed by HVO 2023-10-04 10:32:30 -07:00
hugetlb_vmemmap.h mm: hugetlb: skip initialization of gigantic tail struct pages if freed by HVO 2023-10-04 10:32:30 -07:00
hugetlb.c hugetlb: memcg: account hugetlb-backed memory in memory controller 2023-10-18 14:34:17 -07:00
hwpoison-inject.c
init-mm.c mm: move dummy_vm_ops out of a header 2023-08-21 13:37:46 -07:00
internal.h mm: add printf attribute to shrinker_debugfs_name_alloc 2023-10-18 14:34:18 -07:00
interval_tree.c
io-mapping.c
ioremap.c mm: ioremap: remove unneeded ioremap_allowed and iounmap_allowed 2023-08-18 10:12:36 -07:00
Kconfig zswap: change zswap's default allocator to zsmalloc 2023-10-04 10:32:20 -07:00
Kconfig.debug mm: page_table_check: Make it dependent on EXCLUSIVE_SYSTEM_RAM 2023-05-29 16:14:28 +01:00
khugepaged.c - Some swap cleanups from Ma Wupeng ("fix WARN_ON in add_to_avail_list") 2023-08-29 14:25:26 -07:00
kmemleak.c mm/kmemleak: move up cond_resched() call in page scanning loop 2023-09-02 15:17:34 -07:00
ksm.c mm/ksm: add pages_skipped metric 2023-10-16 15:44:39 -07:00
list_lru.c
maccess.c mm: Fix copy_from_user_nofault(). 2023-04-12 17:36:23 -07:00
madvise.c mm: remove remnants of SPLIT_RSS_COUNTING 2023-10-04 10:32:20 -07:00
Makefile mm: vmscan: move shrinker-related code into a separate file 2023-10-04 10:32:23 -07:00
mapping_dirty_helpers.c mm: fix clean_record_shared_mapping_range kernel-doc 2023-08-24 16:20:30 -07:00
memblock.c memblock: introduce MEMBLOCK_RSRV_NOINIT flag 2023-10-04 10:32:30 -07:00
memcontrol.c hugetlb: memcg: account hugetlb-backed memory in memory controller 2023-10-18 14:34:17 -07:00
memfd.c memfd: drop warning for missing exec-related flags 2023-10-04 10:32:22 -07:00
memory_hotplug.c mm/memory_hotplug: use pfn math in place of direct struct page manipulation 2023-10-04 10:32:29 -07:00
memory-failure.c mm: convert DAX lock/unlock page to lock/unlock folio 2023-10-04 10:32:20 -07:00
memory-tiers.c dax, kmem: calculate abstract distance with general interface 2023-10-16 15:44:39 -07:00
memory.c mm/gup: adapt get_user_page_vma_remote() to never return NULL 2023-10-18 14:34:15 -07:00
mempolicy.c Merge mm-hotfixes-stable into mm-stable to pick up depended-upon changes. 2023-10-18 14:32:58 -07:00
mempool.c mempool: do not use ksize() for poisoning 2022-11-30 15:58:41 -08:00
memremap.c mm/memremap.c: fix outdated comment in devm_memremap_pages 2023-02-09 16:51:46 -08:00
memtest.c mm: memtest: convert to memtest_report_meminfo() 2023-08-21 13:37:47 -07:00
migrate_device.c Add x86 shadow stack support 2023-08-31 12:20:12 -07:00
migrate.c hugetlb: memcg: account hugetlb-backed memory in memory controller 2023-10-18 14:34:17 -07:00
mincore.c mm: enable page walking API to lock vmas during the walk 2023-08-21 13:07:20 -07:00
mlock.c mm: mlock: update mlock_pte_range to handle large folio 2023-10-04 10:32:32 -07:00
mm_init.c mm: hugetlb: skip initialization of gigantic tail struct pages if freed by HVO 2023-10-04 10:32:30 -07:00
mm_slot.h
mmap_lock.c
mmap.c mmap: add clarifying comment to vma_merge() code 2023-10-18 14:34:15 -07:00
mmu_gather.c mm: fix kernel-doc warning from tlb_flush_rmaps() 2023-08-24 16:20:30 -07:00
mmu_notifier.c mmu_notifiers: rename invalidate_range notifier 2023-08-18 10:12:41 -07:00
mmzone.c
mprotect.c mm/mprotect: allow unfaulted VMAs to be unaccounted on mprotect() 2023-10-18 14:34:18 -07:00
mremap.c mm/mremap: allow moves within the same VMA for stack moves 2023-10-04 10:32:20 -07:00
msync.c
nommu.c mm: make __access_remote_vm() static 2023-10-18 14:34:15 -07:00
oom_kill.c mm: remove redundant K() macro definition 2023-08-21 13:37:44 -07:00
page_alloc.c mm/page_alloc: remove unnecessary next_page in break_down_buddy_pages 2023-10-18 14:34:15 -07:00
page_counter.c
page_ext.c mm/page_ext: move functions around for minor cleanups to page_ext 2023-08-18 10:12:31 -07:00
page_idle.c mm: page_idle: convert page idle to use a folio 2023-01-18 17:12:52 -08:00
page_io.c mm: memcg: add THP swap out info for anonymous reclaim 2023-10-04 10:32:27 -07:00
page_isolation.c mm/hugetlb: get rid of page_hstate() 2023-08-18 10:12:39 -07:00
page_owner.c mm/page_ext: use page_ext_data helper in page_owner 2023-08-21 13:37:27 -07:00
page_poison.c mm/page_poison: remove unused page_ext.h from page_poison 2023-08-21 13:37:30 -07:00
page_reporting.c mm, treewide: redefine MAX_ORDER sanely 2023-04-05 19:42:46 -07:00
page_reporting.h
page_table_check.c mm: convert page_table_check_pte_set() to page_table_check_ptes_set() 2023-08-24 16:20:18 -07:00
page_vma_mapped.c mm: correct stale comment of function check_pte 2023-08-18 10:12:13 -07:00
page-writeback.c mm: use folio_xor_flags_has_waiters() in folio_end_writeback() 2023-10-18 14:34:17 -07:00
pagewalk.c mm/pagewalk: fix bootstopping regression from extra pte_unmap() 2023-09-02 08:39:21 -07:00
percpu-internal.h percpu-internal/pcpu_chunk: re-layout pcpu_chunk structure to reduce false sharing 2023-06-19 16:19:29 -07:00
percpu-km.c
percpu-stats.c
percpu-vm.c
percpu.c mm/percpu.c: print error message too if atomic alloc failed 2023-08-25 08:04:59 -07:00
pgalloc-track.h
pgtable-generic.c mm/pgtable: notes on pte_offset_map[_lock]() 2023-08-18 10:12:25 -07:00
process_vm_access.c mm/gup: remove unused vmas parameter from pin_user_pages_remote() 2023-06-09 16:25:25 -07:00
ptdump.c mm: ptdump should use ptep_get_lockless() 2023-06-19 16:19:24 -07:00
readahead.c filemap: Allow __filemap_get_folio to allocate large folios 2023-07-24 18:04:30 -04:00
rmap.c mm/rmap: convert page_move_anon_rmap() to folio_move_anon_rmap() 2023-10-18 14:34:14 -07:00
rodata_test.c
secretmem.c mm/secretmem: use a folio in secretmem_fault() 2023-08-21 13:38:02 -07:00
shmem_quota.c shmem: Add default quota limit mount options 2023-08-09 09:15:40 +02:00
shmem.c shmem,percpu_counter: add _limited_add(fbc, limit, amount) 2023-10-18 14:34:14 -07:00
show_mem.c mm: refactor si_mem_available() 2023-10-04 10:32:19 -07:00
shrinker_debug.c mm: shrinker: convert shrinker_rwsem to mutex 2023-10-04 10:32:26 -07:00
shrinker.c mm: shrinker: convert shrinker_rwsem to mutex 2023-10-04 10:32:26 -07:00
shuffle.c
shuffle.h mm, treewide: redefine MAX_ORDER sanely 2023-04-05 19:42:46 -07:00
slab_common.c slab fixes for 6.6-rc4 2023-09-29 12:10:12 -07:00
slab.c Randomized slab caches for kmalloc() 2023-07-18 10:07:47 +02:00
slab.h Randomized slab caches for kmalloc() 2023-07-18 10:07:47 +02:00
slub.c mm/slub: remove freelist_dereference() 2023-07-14 09:57:21 +02:00
sparse-vmemmap.c mm/vmemmap: allow architectures to override how vmemmap optimization works 2023-08-18 10:12:53 -07:00
sparse.c mm/sparse: remove redundant judgments from macro for_each_present_section_nr 2023-08-18 10:12:14 -07:00
swap_cgroup.c
swap_slots.c
swap_state.c mm/swap: inline folio_set_swap_entry() and folio_swap_entry() 2023-08-24 16:20:28 -07:00
swap.c mm: remove references to pagevec 2023-06-23 16:59:30 -07:00
swap.h swap: remove remnants of polling from read_swap_cache_async 2023-08-24 16:20:16 -07:00
swapfile.c mm/swap: inline folio_set_swap_entry() and folio_swap_entry() 2023-08-24 16:20:28 -07:00
truncate.c - Some swap cleanups from Ma Wupeng ("fix WARN_ON in add_to_avail_list") 2023-08-29 14:25:26 -07:00
usercopy.c mm: Fix copy_from_user_nofault(). 2023-04-12 17:36:23 -07:00
userfaultfd.c Add x86 shadow stack support 2023-08-31 12:20:12 -07:00
util.c rcu: dump vmalloc memory info safely 2023-09-05 10:13:45 -07:00
vmalloc.c mm: hugetlb: add huge page size param to set_huge_pte_at() 2023-09-29 17:20:47 -07:00
vmpressure.c net-memcg: Fix scope of sockmem pressure indicators 2023-08-16 12:21:32 +01:00
vmscan.c mm: multi-gen LRU: reuse some legacy trace events 2023-10-18 14:34:14 -07:00
vmstat.c mm/vmstat: use this_cpu_try_cmpxchg in mod_{zone,node}_state 2023-10-04 10:32:20 -07:00
workingset.c mm: workingset: dynamically allocate the mm-shadow shrinker 2023-10-04 10:32:24 -07:00
z3fold.c mm/z3fold: remove obsolete comment for struct z3fold_pool 2023-08-21 13:37:51 -07:00
zbud.c mm: zswap: remove shrink from zpool interface 2023-06-19 16:19:27 -07:00
zpool.c mm: zswap: remove shrink from zpool interface 2023-06-19 16:19:27 -07:00
zsmalloc.c zsmalloc: use copy_page for full page copy 2023-10-18 14:34:16 -07:00
zswap.c mm: zswap: fix pool refcount bug around shrink_worker() 2023-10-18 12:12:40 -07:00