+ mm-thp-clearpagedoublemap-in-first-page_add_file_rmap.patch added to -mm tree

+ mm-thp-clearpagedoublemap-in-first-page_add_file_rmap.patch added to -mm tree

[Andrew Morton]

The patch titled
     Subject: mm/thp: ClearPageDoubleMap in first page_add_file_rmap()
has been added to the -mm tree.  Its filename is
     mm-thp-clearpagedoublemap-in-first-page_add_file_rmap.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-thp-clearpagedoublemap-in-first-page_add_file_rmap.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-clearpagedoublemap-in-first-page_add_file_rmap.patch

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The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Hugh Dickins <hughd@google.com>
Subject: 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>
---

 mm/rmap.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/mm/rmap.c~mm-thp-clearpagedoublemap-in-first-page_add_file_rmap
+++ a/mm/rmap.c
@@ -1252,6 +1252,17 @@ void page_add_file_rmap(struct page *pag
 		}
 		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);
_

Patches currently in -mm which might be from hughd@google.com are

memfd-fix-f_seal_write-after-shmem-huge-page-allocated.patch
tmpfs-support-for-file-creation-time-fix.patch
mm-thp-clearpagedoublemap-in-first-page_add_file_rmap.patch