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 Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ 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 -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html