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 <[email protected]> > Signed-off-by: Vlastimil Babka <[email protected]> > Reviewed-by: Naoya Horiguchi <[email protected]> > Cc: Minchan Kim <[email protected]> > Cc: Mel Gorman <[email protected]> > Cc: Bartlomiej Zolnierkiewicz <[email protected]> > Cc: Michal Nazarewicz <[email protected]>
Acked-by: Michal Nazarewicz <[email protected]> > Cc: Christoph Lameter <[email protected]> > Cc: Rik van Riel <[email protected]> > --- > 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 +--<[email protected]>--<xmpp:[email protected]>--ooO--(_)--Ooo--
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