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authorHugh Dickins <hughd@google.com>2022-02-14 18:31:48 -0800
committerMatthew Wilcox (Oracle) <willy@infradead.org>2022-02-17 11:57:02 -0500
commit34b6792380ce4f4b41018351cd67c9c26f4a7a0d (patch)
tree8fe823dca2e14be9871318630740fd42372d3fa6 /mm/internal.h
parent07ca760673088f262da57ff42c15558688565aa2 (diff)
mm/munlock: mlock_pte_range() when mlocking or munlocking
Fill in missing pieces: reimplementation of munlock_vma_pages_range(), required to lower the mlock_counts when munlocking without munmapping; and its complement, implementation of mlock_vma_pages_range(), required to raise the mlock_counts on pages already there when a range is mlocked. Combine them into just the one function mlock_vma_pages_range(), using walk_page_range() to run mlock_pte_range(). This approach fixes the "Very slow unlockall()" of unpopulated PROT_NONE areas, reported in https://lore.kernel.org/linux-mm/70885d37-62b7-748b-29df-9e94f3291736@gmail.com/ Munlock clears VM_LOCKED at the start, under exclusive mmap_lock; but if a racing truncate or holepunch (depending on i_mmap_rwsem) gets to the pte first, it will not try to munlock the page: leaving release_pages() to correct it when the last reference to the page is gone - that's okay, a page is not evictable anyway while it is held by an extra reference. Mlock sets VM_LOCKED at the start, under exclusive mmap_lock; but if a racing remove_migration_pte() or try_to_unmap_one() (depending on i_mmap_rwsem) gets to the pte first, it will try to mlock the page, then mlock_pte_range() mlock it a second time. This is harder to reproduce, but a more serious race because it could leave the page unevictable indefinitely though the area is munlocked afterwards. Guard against it by setting the (inappropriate) VM_IO flag, and modifying mlock_vma_page() to decline such vmas. Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Diffstat (limited to 'mm/internal.h')
-rw-r--r--mm/internal.h3
1 files changed, 2 insertions, 1 deletions
diff --git a/mm/internal.h b/mm/internal.h
index a43d79335c16..b3f0dd3ffba2 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -412,7 +412,8 @@ void mlock_page(struct page *page);
static inline void mlock_vma_page(struct page *page,
struct vm_area_struct *vma, bool compound)
{
- if (unlikely(vma->vm_flags & VM_LOCKED) &&
+ /* VM_IO check prevents migration from double-counting during mlock */
+ if (unlikely((vma->vm_flags & (VM_LOCKED|VM_IO)) == VM_LOCKED) &&
(compound || !PageTransCompound(page)))
mlock_page(page);
}