The patch titled
Subject: mm: migrate: fix THP's mapcount on isolation
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-migrate-fix-thps-mapcount-on-isolation.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate-fix-thps-mapcount-on-isolation.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Gavin Shan <gshan@xxxxxxxxxx>
Subject: mm: migrate: fix THP's mapcount on isolation
Date: Thu, 24 Nov 2022 17:55:23 +0800
The issue is reported when removing memory through virtio_mem device. The
transparent huge page, experienced copy-on-write fault, is wrongly
regarded as pinned. The transparent huge page is escaped from being
isolated in isolate_migratepages_block(). The transparent huge page can't
be migrated and the corresponding memory block can't be put into offline
state.
Fix it by replacing page_mapcount() with total_mapcount(). With this, the
transparent huge page can be isolated and migrated, and the memory block
can be put into offline state. Besides, The page's refcount is increased
a bit earlier to avoid the page is released when the check is executed.
Link: https://lkml.kernel.org/r/20221124095523.31061-1-gshan@xxxxxxxxxx
Fixes: 1da2f328fa64 ("mm,thp,compaction,cma: allow THP migration for CMA allocations")
Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
Reported-by: Zhenyu Zhang <zhenyzha@xxxxxxxxxx>
Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: William Kucharski <william.kucharski@xxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [5.7+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/compaction.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
--- a/mm/compaction.c~mm-migrate-fix-thps-mapcount-on-isolation
+++ a/mm/compaction.c
@@ -985,28 +985,28 @@ isolate_migratepages_block(struct compac
}
/*
+ * Be careful not to clear PageLRU until after we're
+ * sure the page is not being freed elsewhere -- the
+ * page release code relies on it.
+ */
+ if (unlikely(!get_page_unless_zero(page)))
+ goto isolate_fail;
+
+ /*
* Migration will fail if an anonymous page is pinned in memory,
* so avoid taking lru_lock and isolating it unnecessarily in an
* admittedly racy check.
*/
mapping = page_mapping(page);
- if (!mapping && page_count(page) > page_mapcount(page))
- goto isolate_fail;
+ if (!mapping && (page_count(page) - 1) > total_mapcount(page))
+ goto isolate_fail_put;
/*
* Only allow to migrate anonymous pages in GFP_NOFS context
* because those do not depend on fs locks.
*/
if (!(cc->gfp_mask & __GFP_FS) && mapping)
- goto isolate_fail;
-
- /*
- * Be careful not to clear PageLRU until after we're
- * sure the page is not being freed elsewhere -- the
- * page release code relies on it.
- */
- if (unlikely(!get_page_unless_zero(page)))
- goto isolate_fail;
+ goto isolate_fail_put;
/* Only take pages on LRU: a check now makes later tests safe */
if (!PageLRU(page))
_
Patches currently in -mm which might be from gshan@xxxxxxxxxx are
mm-migrate-fix-thps-mapcount-on-isolation.patch
