The patch titled
Subject: mm: compaction: do not accidentally skip pageblocks in the migrate scanner
has been added to the -mm tree. Its filename is
mm-compaction-do-not-accidentally-skip-pageblocks-in-the-migrate-scanner.patch
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From: Mel Gorman <mgorman@xxxxxxx>
Subject: mm: compaction: do not accidentally skip pageblocks in the migrate scanner
Compaction uses the ALIGN macro incorrectly with the migrate scanner by
adding pageblock_nr_pages to a PFN. It happened to work when initially
implemented as the starting PFN was also aligned but with caching restarts
and isolating in smaller chunks this is no longer always true.
The impact is that the migrate scanner scans outside its current
pageblock. As pfn_valid() is still checked properly it does not cause any
failure and the impact of the bug is that in some cases it will scan more
than necessary when it crosses a page boundary but by no more than
COMPACT_CLUSTER_MAX. It is highly unlikely this is even measurable but
it's still wrong so this patch addresses the problem.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/compaction.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff -puN mm/compaction.c~mm-compaction-do-not-accidentally-skip-pageblocks-in-the-migrate-scanner mm/compaction.c
--- a/mm/compaction.c~mm-compaction-do-not-accidentally-skip-pageblocks-in-the-migrate-scanner
+++ a/mm/compaction.c
@@ -597,8 +597,7 @@ check_compact_cluster:
continue;
next_pageblock:
- low_pfn += pageblock_nr_pages;
- low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
+ low_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages) - 1;
last_pageblock_nr = pageblock_nr;
}
@@ -781,7 +780,7 @@ static isolate_migrate_t isolate_migrate
low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
/* Only scan within a pageblock boundary */
- end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
+ end_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages);
/* Do not cross the free scanner or scan within a memory hole */
if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
_
Patches currently in -mm which might be from mgorman@xxxxxxx are
origin.patch
linux-next.patch
mm-cond_resched-in-tlb_flush_mmu-to-fix-soft-lockups-on-config_preempt.patch
mm-fix-zone_watermark_ok_safe-accounting-of-isolated-pages.patch
mm-memcg-only-evict-file-pages-when-we-have-plenty.patch
mm-vmscan-save-work-scanning-almost-empty-lru-lists.patch
mm-vmscan-clarify-how-swappiness-highest-priority-memcg-interact.patch
mm-vmscan-improve-comment-on-low-page-cache-handling.patch
mm-vmscan-clean-up-get_scan_count.patch
mm-vmscan-clean-up-get_scan_count-fix.patch
mm-vmscan-compaction-works-against-zones-not-lruvecs.patch
mm-vmscan-compaction-works-against-zones-not-lruvecs-fix.patch
mm-reduce-rmap-overhead-for-ex-ksm-page-copies-created-on-swap-faults.patch
mm-page_allocc-__setup_per_zone_wmarks-make-min_pages-unsigned-long.patch
mm-vmscanc-__zone_reclaim-replace-max_t-with-max.patch
mm-compaction-do-not-accidentally-skip-pageblocks-in-the-migrate-scanner.patch
mm-memmap_init_zone-performance-improvement.patch
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