Messages in this thread | | | From | Michal Nazarewicz <> | Subject | Re: [PATCH v2] mm, compaction: properly signal and act upon lock and need_sched() contention | Date | Fri, 16 May 2014 10:33:35 -0700 |
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On Fri, May 16 2014, Vlastimil Babka wrote: > Compaction uses compact_checklock_irqsave() function to periodically check for > lock contention and need_resched() to either abort async compaction, or to > free the lock, schedule and retake the lock. When aborting, cc->contended is > set to signal the contended state to the caller. Two problems have been > identified in this mechanism. > > First, compaction also calls directly cond_resched() in both scanners when no > lock is yet taken. This call either does not abort async compaction, or set > cc->contended appropriately. This patch introduces a new compact_should_abort() > function to achieve both. In isolate_freepages(), the check frequency is > reduced to once by SWAP_CLUSTER_MAX pageblocks to match what the migration > scanner does in the preliminary page checks. In case a pageblock is found > suitable for calling isolate_freepages_block(), the checks within there are > done on higher frequency. > > Second, isolate_freepages() does not check if isolate_freepages_block() > aborted due to contention, and advances to the next pageblock. This violates > the principle of aborting on contention, and might result in pageblocks not > being scanned completely, since the scanning cursor is advanced. This patch > makes isolate_freepages_block() check the cc->contended flag and abort. > > In case isolate_freepages() has already isolated some pages before aborting > due to contention, page migration will proceed, which is OK since we do not > want to waste the work that has been done, and page migration has own checks > for contention. However, we do not want another isolation attempt by either > of the scanners, so cc->contended flag check is added also to > compaction_alloc() and compact_finished() to make sure compaction is aborted > right after the migration. > > Reported-by: Joonsoo Kim <iamjoonsoo.kim@lge.com> > Signed-off-by: Vlastimil Babka <vbabka@suse.cz> > Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > Cc: Minchan Kim <minchan@kernel.org> > Cc: Mel Gorman <mgorman@suse.de> > Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> > Cc: Michal Nazarewicz <mina86@mina86.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
> Cc: Christoph Lameter <cl@linux.com> > Cc: Rik van Riel <riel@redhat.com> > --- > v2: update struct compact_control comment (per Naoya Horiguchi) > rename to compact_should_abort() and add comments (per David Rientjes) > add cc->contended checks in compaction_alloc() and compact_finished() > (per Joonsoo Kim) > reduce frequency of checks in isolate_freepages() > -- Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o ..o | Computer Science, Michał “mina86” Nazarewicz (o o) ooo +--<mpn@google.com>--<xmpp:mina86@jabber.org>--ooO--(_)--Ooo-- [unhandled content-type:application/pgp-signature] | |