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authorHugh Dickins <hughd@google.com>2022-03-22 14:47:40 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-03-22 15:57:11 -0700
commitbd55b0c2d64e84a75575f548a33a3dfecc135b65 (patch)
tree5058ecd90eded623d985eca96a08d9ce664b8ffb /mm/rmap.c
parent734c15700cdf9062ae98d8b131c6fe873dfad26d (diff)
mm/thp: ClearPageDoubleMap in first page_add_file_rmap()
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: 9a73f61bdb8a ("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>
Diffstat (limited to 'mm/rmap.c')
-rw-r--r--mm/rmap.c11
1 files changed, 11 insertions, 0 deletions
diff --git a/mm/rmap.c b/mm/rmap.c
index 09b08888120e..66cb69c1c5dd 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1252,6 +1252,17 @@ void page_add_file_rmap(struct page *page, bool compound)
}
if (!atomic_inc_and_test(compound_mapcount_ptr(page)))
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))
__mod_lruvec_page_state(page, NR_SHMEM_PMDMAPPED,
nr_pages);