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linux/mm
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Oscar Salvador ea2c3f6f55 mm,mremap: bail out earlier in mremap_to under map pressure 
When using mremap() syscall in addition to MREMAP_FIXED flag, mremap()
calls mremap_to() which does the following:

1) unmaps the destination region where we are going to move the map
2) If the new region is going to be smaller, we unmap the last part
   of the old region

Then, we will eventually call move_vma() to do the actual move.

move_vma() checks whether we are at least 4 maps below max_map_count
before going further, otherwise it bails out with -ENOMEM.  The problem
is that we might have already unmapped the vma's in steps 1) and 2), so
it is not possible for userspace to figure out the state of the vmas
after it gets -ENOMEM, and it gets tricky for userspace to clean up
properly on error path.

While it is true that we can return -ENOMEM for more reasons (e.g: see
may_expand_vm() or move_page_tables()), I think that we can avoid this
scenario if we check early in mremap_to() if the operation has high
chances to succeed map-wise.

Should that not be the case, we can bail out before we even try to unmap
anything, so we make sure the vma's are left untouched in case we are
likely to be short of maps.

The thumb-rule now is to rely on the worst-scenario case we can have.
That is when both vma's (old region and new region) are going to be
split in 3, so we get two more maps to the ones we already hold (one per
each).  If current map count + 2 maps still leads us to 4 maps below the
threshold, we are going to pass the check in move_vma().

Of course, this is not free, as it might generate false positives when
it is true that we are tight map-wise, but the unmap operation can
release several vma's leading us to a good state.

Another approach was also investigated [1], but it may be too much
hassle for what it brings.

[1] https://lore.kernel.org/lkml/20190219155320.tkfkwvqk53tfdojt@d104.suse.de/

Link: http://lkml.kernel.org/r/20190226091314.18446-1-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-03-05 21:07:21 -08:00
..
kasan kasan: fix coccinelle warnings in kasan_p*_table 2019-03-05 21:07:13 -08:00
backing-dev.c writeback: synchronize sync(2) against cgroup writeback membership switches 2019-01-22 14:39:38 -07:00
balloon_compaction.c virtio_balloon: fix deadlock on OOM 2017-11-14 23:57:38 +02:00
cleancache.c mm: use octal not symbolic permissions 2018-06-15 07:55:25 +09:00
cma_debug.c mm/cma_debug.c: remove static scoped cma_debugfs_root 2019-03-05 21:07:20 -08:00
cma.c mm/cma.c: cma_declare_contiguous: correct err handling 2019-03-05 21:07:21 -08:00
cma.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
compaction.c mm/compaction: pass pgdat to too_many_isolated() instead of zone 2019-03-05 21:07:21 -08:00
debug_page_ref.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
debug.c mm/debug.c: fix __dump_page() for poisoned pages 2019-02-21 09:01:00 -08:00
dmapool.c docs/core-api/mm: fix return value descriptions in mm/ 2019-03-05 21:07:20 -08:00
early_ioremap.c mm/early_ioremap: Fix boot hang with earlyprintk=efi,keep 2017-12-11 14:54:44 +01:00
fadvise.c vfs: implement readahead(2) using POSIX_FADV_WILLNEED 2018-08-30 20:01:32 +02:00
failslab.c mm: no need to check return value of debugfs_create functions 2019-03-05 21:07:17 -08:00
filemap.c mm: remove zone_lru_lock() function, access ->lru_lock directly 2019-03-05 21:07:21 -08:00
frame_vector.c mm/frame_vector.c: release a semaphore in 'get_vaddr_frames()' 2017-12-14 16:00:48 -08:00
frontswap.c mm: use octal not symbolic permissions 2018-06-15 07:55:25 +09:00
gup_benchmark.c mm: no need to check return value of debugfs_create functions 2019-03-05 21:07:17 -08:00
gup.c mm: update get_user_pages_longterm to migrate pages allocated from CMA region 2019-03-05 21:07:19 -08:00
highmem.c mm: convert totalram_pages and totalhigh_pages variables to atomic 2018-12-28 12:11:47 -08:00
hmm.c mm/hmm: fix memremap.h, move dev_page_fault_t callback to hmm 2018-12-28 12:11:52 -08:00
huge_memory.c mm/huge_memory.c: fix "orig_pud" set but not used 2019-03-05 21:07:21 -08:00
hugetlb_cgroup.c mm: rename page_counter's count/limit into usage/max 2018-06-07 17:34:35 -07:00
hugetlb.c mm: update get_user_pages_longterm to migrate pages allocated from CMA region 2019-03-05 21:07:19 -08:00
hwpoison-inject.c mm/memory_failure: Remove unused trapno from memory_failure 2018-01-23 12:17:42 -06:00
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, compaction: capture a page under direct compaction 2019-03-05 21:07:17 -08:00
interval_tree.c mm/interval_tree.c: use vma_pages() helper 2018-01-31 17:18:37 -08:00
Kconfig ksm: replace jhash2 with xxhash 2018-12-28 12:11:46 -08:00
Kconfig.debug mm/page_owner: move config option to mm/Kconfig.debug 2019-03-05 21:07:18 -08:00
khugepaged.c mm: memcontrol: expose THP events on a per-memcg basis 2019-03-05 21:07:19 -08:00
kmemleak-test.c
kmemleak.c kmemleak: account for tagged pointers when calculating pointer range 2019-02-21 09:01:00 -08:00
ksm.c mm: ksm: do not block on page lock when searching stable tree 2019-03-05 21:07:19 -08:00
list_lru.c numa: make "nr_node_ids" unsigned int 2019-03-05 21:07:19 -08:00
maccess.c Revert "x86/fault: BUG() when uaccess helpers fault on kernel addresses" 2019-02-25 09:10:51 -08:00
madvise.c mm/mmu_notifier: use structure for invalidate_range_start/end calls v2 2018-12-28 12:11:50 -08:00
Makefile mm: remove nobootmem 2018-10-31 08:54:16 -07:00
memblock.c mm: no need to check return value of debugfs_create functions 2019-03-05 21:07:17 -08:00
memcontrol.c mm/memcontrol.c: fix bad line in comment 2019-03-05 21:07:21 -08:00
memfd.c mm/memfd: add an F_SEAL_FUTURE_WRITE seal to memfd 2019-03-05 21:07:19 -08:00
memory_hotplug.c mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC 2019-03-05 21:07:21 -08:00
memory-failure.c mm: hwpoison: fix thp split handing in soft_offline_in_use_page() 2019-03-05 21:07:13 -08:00
memory.c mm/memory.c: do_fault: avoid usage of stale vm_area_struct 2019-03-05 21:07:21 -08:00
mempolicy.c mm, mempolicy: fix uninit memory access 2019-03-05 21:07:18 -08:00
mempool.c docs/core-api/mm: fix return value descriptions in mm/ 2019-03-05 21:07:20 -08:00
memtest.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
migrate.c mm/migrate.c: cleanup expected_page_refs() 2019-03-05 21:07:20 -08:00
mincore.c Revert "Change mincore() to count "mapped" pages rather than "cached" pages" 2019-01-24 09:04:37 +13:00
mlock.c mm: remove zone_lru_lock() function, access ->lru_lock directly 2019-03-05 21:07:21 -08:00
mm_init.c mm: convert totalram_pages and totalhigh_pages variables to atomic 2018-12-28 12:11:47 -08:00
mmap.c mm: fix some typos in mm directory 2019-03-05 21:07:18 -08:00
mmu_context.c
mmu_gather.c mm: Replace call_rcu_sched() with call_rcu() 2018-11-27 09:21:46 -08:00
mmu_notifier.c mm/mmu_notifier: use structure for invalidate_range_start/end calls v2 2018-12-28 12:11:50 -08:00
mmzone.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
mprotect.c mm: update ptep_modify_prot_commit to take old pte value as arg 2019-03-05 21:07:18 -08:00
mremap.c mm,mremap: bail out earlier in mremap_to under map pressure 2019-03-05 21:07:21 -08:00
msync.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
nommu.c mm/gup: cache dev_pagemap while pinning pages 2018-10-26 16:38:15 -07:00
oom_kill.c mm,oom: don't kill global init via memory.oom.group 2019-03-05 21:07:19 -08:00
page_alloc.c mm: unexport free_reserved_area 2019-03-05 21:07:20 -08:00
page_counter.c memcg: introduce memory.min 2018-06-07 17:34:36 -07:00
page_ext.c mm/page_ext.c: fix an imbalance with kmemleak 2019-03-05 21:07:21 -08:00
page_idle.c mm: remove zone_lru_lock() function, access ->lru_lock directly 2019-03-05 21:07:21 -08:00
page_io.c mm/page_io.c: fix polled swap page in 2019-01-04 13:13:48 -08:00
page_isolation.c mm: only report isolation failures when offlining memory 2018-12-28 12:11:46 -08:00
page_owner.c mm: no need to check return value of debugfs_create functions 2019-03-05 21:07:17 -08:00
page_poison.c page_poison: play nicely with KASAN 2019-03-05 21:07:13 -08:00
page_vma_mapped.c mm/rmap: map_pte() was not handling private ZONE_DEVICE page properly 2018-10-31 08:54:11 -07:00
page-writeback.c docs/core-api/mm: fix return value descriptions in mm/ 2019-03-05 21:07:20 -08:00
pagewalk.c mm: kernel-doc: add missing parameter descriptions 2018-04-05 21:36:27 -07:00
percpu-internal.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
percpu-km.c percpu: convert spin_lock_irq to spin_lock_irqsave. 2018-12-18 09:04:08 -08:00
percpu-stats.c treewide: Use array_size() in vmalloc() 2018-06-12 16:19:22 -07:00
percpu-vm.c percpu: allow select gfp to be passed to underlying allocators 2018-02-18 05:33:01 -08:00
percpu.c Merge branch 'for-4.20' of git://git.kernel.org/pub/scm/linux/kernel/git/dennis/percpu 2018-11-01 09:27:57 -07:00
pgtable-generic.c x86/mm: Page size aware flush_tlb_mm_range() 2018-10-09 16:51:11 +02:00
process_vm_access.c mm: docs: add blank lines to silence sphinx "Unexpected indentation" errors 2018-02-06 18:32:48 -08:00
quicklist.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
readahead.c docs/core-api/mm: fix return value descriptions in mm/ 2019-03-05 21:07:20 -08:00
rmap.c mm: remove zone_lru_lock() function, access ->lru_lock directly 2019-03-05 21:07:21 -08:00
rodata_test.c
shmem.c mm/memfd: add an F_SEAL_FUTURE_WRITE seal to memfd 2019-03-05 21:07:19 -08:00
slab_common.c docs/core-api/mm: fix return value descriptions in mm/ 2019-03-05 21:07:20 -08:00
slab.c docs/core-api/mm: fix return value descriptions in mm/ 2019-03-05 21:07:20 -08:00
slab.h memcg: localize memcg_kmem_enabled() check 2019-03-05 21:07:15 -08:00
slob.c slab: __GFP_ZERO is incompatible with a constructor 2018-06-07 17:34:34 -07:00
slub.c numa: make "nr_node_ids" unsigned int 2019-03-05 21:07:19 -08:00
sparse-vmemmap.c mm: remove include/linux/bootmem.h 2018-10-31 08:54:16 -07:00
sparse.c mm/sparse: fix a bad comparison 2019-03-05 21:07:21 -08:00
swap_cgroup.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
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 mm: swap: add comment for swap_vma_readahead 2019-03-05 21:07:16 -08:00
swap.c mm: remove zone_lru_lock() function, access ->lru_lock directly 2019-03-05 21:07:21 -08:00
swapfile.c mm/swapfile.c: use struct_size() in kvzalloc() 2019-03-05 21:07:21 -08:00
truncate.c docs/core-api/mm: fix return value descriptions in mm/ 2019-03-05 21:07:20 -08:00
usercopy.c mm/usercopy.c: no check page span for stack objects 2019-01-08 17:15:11 -08:00
userfaultfd.c hugetlbfs: revert "use i_mmap_rwsem for more pmd sharing synchronization" 2019-01-08 17:15:11 -08:00
util.c docs/core-api/mm: fix return value descriptions in mm/ 2019-03-05 21:07:20 -08:00
vmacache.c mm: get rid of vmacache_flush_all() entirely 2018-09-13 15:18:04 -10:00
vmalloc.c docs/core-api/mm: fix return value descriptions in mm/ 2019-03-05 21:07:20 -08:00
vmpressure.c mm/vmpressure.c: convert to use match_string() helper 2018-06-07 17:34:36 -07:00
vmscan.c mm: remove zone_lru_lock() function, access ->lru_lock directly 2019-03-05 21:07:21 -08:00
vmstat.c mm: no need to check return value of debugfs_create functions 2019-03-05 21:07:17 -08:00
workingset.c mm/workingset: remove unused @mapping argument in workingset_eviction() 2019-03-05 21:07:21 -08:00
z3fold.c z3fold: fix possible reclaim races 2018-11-18 10:15:09 -08:00
zbud.c mm: docs: fix parameter names mismatch 2018-02-06 18:32:48 -08:00
zpool.c mm/zpool.c: zpool_evictable: fix mismatch in parameter name and kernel-doc 2018-02-21 15:35:43 -08:00
zsmalloc.c mm/zsmalloc.c: fix fall-through annotation 2018-10-26 16:26:35 -07:00
zswap.c mm: convert totalram_pages and totalhigh_pages variables to atomic 2018-12-28 12:11:47 -08:00