The quilt patch titled
Subject: mm: improve folio_likely_mapped_shared() using the mapcount of large folios
has been removed from the -mm tree. Its filename was
mm-improve-folio_likely_mapped_shared-using-the-mapcount-of-large-folios.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm: improve folio_likely_mapped_shared() using the mapcount of large folios
Date: Tue, 9 Apr 2024 21:22:48 +0200
We can now read the mapcount of large folios very efficiently. Use it to
improve our handling of partially-mappable folios, falling back to making
a guess only in case the folio is not "obviously mapped shared".
We can now better detect partially-mappable folios where the first page is
not mapped as "mapped shared", reducing "false negatives"; but false
negatives are still possible.
While at it, fixup a wrong comment (false positive vs. false negative)
for KSM folios.
Link: https://lkml.kernel.org/r/20240409192301.907377-6-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
Cc: Chris Zankel <chris@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Max Filippov <jcmvbkbc@xxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Naoya Horiguchi <nao.horiguchi@xxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Richard Chang <richardycc@xxxxxxxxxx>
Cc: Rich Felker <dalias@xxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Yoshinori Sato <ysato@xxxxxxxxxxxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
--- a/include/linux/mm.h~mm-improve-folio_likely_mapped_shared-using-the-mapcount-of-large-folios
+++ a/include/linux/mm.h
@@ -2184,7 +2184,7 @@ static inline size_t folio_size(struct f
* indicate "mapped shared" (false positive) when two VMAs in the same MM
* cover the same file range.
* #. For (small) KSM folios, the return value can wrongly indicate "mapped
- * shared" (false negative), when the folio is mapped multiple times into
+ * shared" (false positive), when the folio is mapped multiple times into
* the same MM.
*
* Further, this function only considers current page table mappings that
@@ -2201,7 +2201,22 @@ static inline size_t folio_size(struct f
*/
static inline bool folio_likely_mapped_shared(struct folio *folio)
{
- return page_mapcount(folio_page(folio, 0)) > 1;
+ int mapcount = folio_mapcount(folio);
+
+ /* Only partially-mappable folios require more care. */
+ if (!folio_test_large(folio) || unlikely(folio_test_hugetlb(folio)))
+ return mapcount > 1;
+
+ /* A single mapping implies "mapped exclusively". */
+ if (mapcount <= 1)
+ return false;
+
+ /* If any page is mapped more than once we treat it "mapped shared". */
+ if (folio_entire_mapcount(folio) || mapcount > folio_nr_pages(folio))
+ return true;
+
+ /* Let's guess based on the first subpage. */
+ return atomic_read(&folio->_mapcount) > 0;
}
#ifndef HAVE_ARCH_MAKE_PAGE_ACCESSIBLE
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
