Subject: + mm-compaction-reset-cached-scanner-pfns-before-reading-them.patch added to -mm tree
To: vbabka@xxxxxxx,iamjoonsoo.kim@xxxxxxx,mgorman@xxxxxxx,riel@xxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Wed, 11 Dec 2013 15:43:09 -0800
The patch titled
Subject: mm: compaction: reset cached scanner pfn's before reading them
has been added to the -mm tree. Its filename is
mm-compaction-reset-cached-scanner-pfns-before-reading-them.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-compaction-reset-cached-scanner-pfns-before-reading-them.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-compaction-reset-cached-scanner-pfns-before-reading-them.patch
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From: Vlastimil Babka <vbabka@xxxxxxx>
Subject: mm: compaction: reset cached scanner pfn's before reading them
Compaction caches pfn's for its migrate and free scanners to avoid
scanning the whole zone each time. In compact_zone(), the cached values
are read to set up initial values for the scanners. There are several
situations when these cached pfn's are reset to the first and last pfn of
the zone, respectively. One of these situations is when a compaction has
been deferred for a zone and is now being restarted during a direct
compaction, which is also done in compact_zone().
However, compact_zone() currently reads the cached pfn's *before*
resetting them. This means the reset doesn't affect the compaction that
performs it, and with good chance also subsequent compactions, as
update_pageblock_skip() is likely to be called and update the cached pfn's
to those being processed. Another chance for a successful reset is when a
direct compaction detects that migration and free scanners meet (which has
its own problems addressed by another patch) and sets
update_pageblock_skip flag which kswapd uses to do the reset because it
goes to sleep.
This is clearly a bug that results in non-deterministic behavior, so this
patch moves the cached pfn reset to be performed *before* the values are
read.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/compaction.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
diff -puN mm/compaction.c~mm-compaction-reset-cached-scanner-pfns-before-reading-them mm/compaction.c
--- a/mm/compaction.c~mm-compaction-reset-cached-scanner-pfns-before-reading-them
+++ a/mm/compaction.c
@@ -943,6 +943,14 @@ static int compact_zone(struct zone *zon
}
/*
+ * Clear pageblock skip if there were failures recently and compaction
+ * is about to be retried after being deferred. kswapd does not do
+ * this reset as it'll reset the cached information when going to sleep.
+ */
+ if (compaction_restarting(zone, cc->order) && !current_is_kswapd())
+ __reset_isolation_suitable(zone);
+
+ /*
* Setup to move all movable pages to the end of the zone. Used cached
* information on where the scanners should start but check that it
* is initialised by ensuring the values are within zone boundaries.
@@ -958,14 +966,6 @@ static int compact_zone(struct zone *zon
zone->compact_cached_migrate_pfn = cc->migrate_pfn;
}
- /*
- * Clear pageblock skip if there were failures recently and compaction
- * is about to be retried after being deferred. kswapd does not do
- * this reset as it'll reset the cached information when going to sleep.
- */
- if (compaction_restarting(zone, cc->order) && !current_is_kswapd())
- __reset_isolation_suitable(zone);
-
trace_mm_compaction_begin(start_pfn, cc->migrate_pfn, cc->free_pfn, end_pfn);
migrate_prep_local();
_
Patches currently in -mm which might be from vbabka@xxxxxxx are
mm-mmapc-add-mlock_future_check-helper.patch
mm-mlock-prepare-params-outside-critical-region.patch
mm-compaction-trace-compaction-begin-and-end.patch
mm-compaction-encapsulate-defer-reset-logic.patch
mm-compaction-reset-cached-scanner-pfns-before-reading-them.patch
mm-compaction-detect-when-scanners-meet-in-isolate_freepages.patch
mm-compaction-do-not-mark-unmovable-pageblocks-as-skipped-in-async-compaction.patch
mm-compaction-reset-scanner-positions-immediately-when-they-meet.patch
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