The patch titled
Subject: mm: compaction: check pfn_valid when entering a new MAX_ORDER_NR_PAGES block during isolation for migration
has been added to the -mm tree. Its filename is
mm-compaction-check-pfn_valid-when-entering-a-new-max_order_nr_pages-block-during-isolation-for-migration.patch
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From: Mel Gorman <mgorman@xxxxxxx>
Subject: mm: compaction: check pfn_valid when entering a new MAX_ORDER_NR_PAGES block during isolation for migration
When isolating for migration, migration starts at the start of a zone
which is not necessarily pageblock aligned. Further, it stops isolating
when COMPACT_CLUSTER_MAX pages are isolated so migrate_pfn is generally
not aligned.
The problem is that pfn_valid is only called on the first PFN being
checked. Lets say we have a case like this
H = MAX_ORDER_NR_PAGES boundary
| = pageblock boundary
m = cc->migrate_pfn
f = cc->free_pfn
o = memory hole
H------|------H------|----m-Hoooooo|ooooooH-f----|------H
The migrate_pfn is just below a memory hole and the free scanner is beyond
the hole. When isolate_migratepages started, it scans from migrate_pfn to
migrate_pfn+pageblock_nr_pages which is now in a memory hole. It checks
pfn_valid() on the first PFN but then scans into the hole where there are
not necessarily valid struct pages.
This patch ensures that isolate_migratepages calls pfn_valid when
necessary.
Reported-and-tested-by: Herbert van den Bergh <herbert.van.den.bergh@xxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/compaction.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff -puN mm/compaction.c~mm-compaction-check-pfn_valid-when-entering-a-new-max_order_nr_pages-block-during-isolation-for-migration mm/compaction.c
--- a/mm/compaction.c~mm-compaction-check-pfn_valid-when-entering-a-new-max_order_nr_pages-block-during-isolation-for-migration
+++ a/mm/compaction.c
@@ -313,6 +313,19 @@ static isolate_migrate_t isolate_migrate
} else if (!locked)
spin_lock_irq(&zone->lru_lock);
+ /*
+ * migrate_pfn does not necessarily start aligned to a
+ * pageblock. Ensure that pfn_valid is called when moving
+ * into a new MAX_ORDER_NR_PAGES range in case of large
+ * memory holes within the zone
+ */
+ if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
+ if (!pfn_valid(low_pfn)) {
+ low_pfn += MAX_ORDER_NR_PAGES - 1;
+ continue;
+ }
+ }
+
if (!pfn_valid_within(low_pfn))
continue;
nr_scanned++;
_
Subject: Subject: mm: compaction: check pfn_valid when entering a new MAX_ORDER_NR_PAGES block during isolation for migration
Patches currently in -mm which might be from mgorman@xxxxxxx are
origin.patch
mm-compaction-check-pfn_valid-when-entering-a-new-max_order_nr_pages-block-during-isolation-for-migration.patch
mm-vmscan-fix-misused-nr_reclaimed-in-shrink_mem_cgroup_zone.patch
make-swapin-readahead-skip-over-holes.patch
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