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mm, fault_around: do not take a reference to a locked page

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filemap_map_pages takes a speculative reference to each page in the range
before it tries to lock that page.  While this is correct it also can
influence page migration which will bail out when seeing an elevated
reference count.  The faultaround code would bail on seeing a locked page
so we can pro-actively check the PageLocked bit before
page_cache_get_speculative and prevent from pointless reference count
churn.

Link: http://lkml.kernel.org/r/20181211142741.2607-4-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Suggested-by: Jan Kara <jack@suse.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michal Hocko 2018-12-28 00:38:36 -08:00 committed by Linus Torvalds
parent bb8965bd82
commit e0975b2aae
1 changed files with 7 additions and 0 deletions
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7
mm/filemap.c
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@ -2614,6 +2614,13 @@ void filemap_map_pages(struct vm_fault *vmf,
goto next;
head = compound_head(page);
/*
* Check for a locked page first, as a speculative
* reference may adversely influence page migration.
*/
if (PageLocked(head))
goto next;
if (!page_cache_get_speculative(head))
goto next;