The patch titled
Subject: mm, fault_around: do not take a reference to a locked page
has been added to the -mm tree. Its filename is
mm-fault_around-do-not-take-a-reference-to-a-locked-page.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-fault_around-do-not-take-a-reference-to-a-locked-page.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-fault_around-do-not-take-a-reference-to-a-locked-page.patch
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------------------------------------------------------
From: Michal Hocko <mhocko@xxxxxxxx>
Subject: mm, fault_around: do not take a reference to a locked page
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@xxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Suggested-by: Jan Kara <jack@xxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/mm/filemap.c~mm-fault_around-do-not-take-a-reference-to-a-locked-page
+++ a/mm/filemap.c
@@ -2652,6 +2652,13 @@ void filemap_map_pages(struct vm_fault *
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;
_
Patches currently in -mm which might be from mhocko@xxxxxxxx are
mm-print-more-information-about-mapping-in-__dump_page.patch
mm-lower-the-printk-loglevel-for-__dump_page-messages.patch
mm-memory_hotplug-drop-pointless-block-alignment-checks-from-__offline_pages.patch
mm-memory_hotplug-print-reason-for-the-offlining-failure.patch
mm-memory_hotplug-be-more-verbose-for-memory-offline-failures.patch
mm-memory_hotplug-be-more-verbose-for-memory-offline-failures-update.patch
mm-memory_hotplug-do-not-clear-numa_node-association-after-hot_remove.patch
hwpoison-memory_hotplug-allow-hwpoisoned-pages-to-be-offlined.patch
mm-proc-be-more-verbose-about-unstable-vma-flags-in-proc-pid-smaps.patch
mm-thp-proc-report-thp-eligibility-for-each-vma.patch
mm-proc-report-pr_set_thp_disable-in-proc.patch
mm-memory_hotplug-try-to-migrate-full-pfn-range.patch
mm-memory_hotplug-deobfuscate-migration-part-of-offlining.patch
mm-fault_around-do-not-take-a-reference-to-a-locked-page.patch
