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mm/thp: ClearPageDoubleMap in first page_add_file_rmap()

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PageDoubleMap is maintained differently for anon and for shmem+file: the
shmem+file one was never cleared, because a safe place to do so could
not be found; so it would blight future use of the cached hugepage until
evicted.

See https://lore.kernel.org/lkml/1571938066-29031-1-git-send-email-yang.shi@linux.alibaba.com/

But page_add_file_rmap() does provide a safe place to do so (though later
than one might wish): allowing testing to return to an initial state
without a damaging drop_caches.

Link: https://lkml.kernel.org/r/61c5cf99-a962-9a25-597a-53ab1bd8fbc0@google.com
Fixes: 9a73f61bdb ("thp, mlock: do not mlock PTE-mapped file huge pages")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2022-03-22 14:47:40 -07:00 • committed by Linus Torvalds
parent 734c15700c
commit bd55b0c2d6
1 changed files with 11 additions and 0 deletions
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11
mm/rmap.c
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@ -1252,6 +1252,17 @@ void page_add_file_rmap(struct page *page, bool compound)
} }
if (!atomic_inc_and_test(compound_mapcount_ptr(page))) if (!atomic_inc_and_test(compound_mapcount_ptr(page)))
goto out; goto out;
/*
* It is racy to ClearPageDoubleMap in page_remove_file_rmap();
* but page lock is held by all page_add_file_rmap() compound
* callers, and SetPageDoubleMap below warns if !PageLocked:
* so here is a place that DoubleMap can be safely cleared.
*/
VM_WARN_ON_ONCE(!PageLocked(page));
if (nr == nr_pages && PageDoubleMap(page))
ClearPageDoubleMap(page);
if (PageSwapBacked(page)) if (PageSwapBacked(page))
__mod_lruvec_page_state(page, NR_SHMEM_PMDMAPPED, __mod_lruvec_page_state(page, NR_SHMEM_PMDMAPPED,
nr_pages); nr_pages);