From: David Rientjes <rientjes@google.com> To: Vlastimil Babka <vbabka@suse.cz> Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>, Greg Thelen <gthelen@google.com>, Minchan Kim <minchan@kernel.org>, Mel Gorman <mgorman@suse.de>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Michal Nazarewicz <mina86@mina86.com>, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, Christoph Lameter <cl@linux.com>, Rik van Riel <riel@redhat.com> Subject: Re: [PATCH 01/10] mm, compaction: do not recheck suitable_migration_target under lock Date: Mon, 9 Jun 2014 16:41:36 -0700 (PDT) [thread overview] Message-ID: <alpine.DEB.2.02.1406091636190.17705@chino.kir.corp.google.com> (raw) In-Reply-To: <1402305982-6928-1-git-send-email-vbabka@suse.cz> On Mon, 9 Jun 2014, Vlastimil Babka wrote: > isolate_freepages_block() rechecks if the pageblock is suitable to be a target > for migration after it has taken the zone->lock. However, the check has been > optimized to occur only once per pageblock, and compact_checklock_irqsave() > might be dropping and reacquiring lock, which means somebody else might have > changed the pageblock's migratetype meanwhile. > > Furthermore, nothing prevents the migratetype to change right after > isolate_freepages_block() has finished isolating. Given how imperfect this is, > it's simpler to just rely on the check done in isolate_freepages() without > lock, and not pretend that the recheck under lock guarantees anything. It is > just a heuristic after all. > > Signed-off-by: Vlastimil Babka <vbabka@suse.cz> > Cc: Minchan Kim <minchan@kernel.org> > Cc: Mel Gorman <mgorman@suse.de> > Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> > Cc: Michal Nazarewicz <mina86@mina86.com> > Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > Cc: Christoph Lameter <cl@linux.com> > Cc: Rik van Riel <riel@redhat.com> > Cc: David Rientjes <rientjes@google.com> Acked-by: David Rientjes <rientjes@google.com> We already do a preliminary check for suitable_migration_target() in isolate_freepages() in a racy way to avoid unnecessary work (and page_order() there is unprotected, I think you already mentioned this) so this seems fine to abandon. > --- > I suggest folding mm-compactionc-isolate_freepages_block-small-tuneup.patch into this > Hmm, Andrew was just moving some code around in that patch, I'm not sure that it makes sense to couple these two together and your patch here is addressing an optimization rather than a cleanup (and you've documented it well, no need to obscure it with unrelated changes).
WARNING: multiple messages have this Message-ID (diff)
From: David Rientjes <rientjes@google.com> To: Vlastimil Babka <vbabka@suse.cz> Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>, Greg Thelen <gthelen@google.com>, Minchan Kim <minchan@kernel.org>, Mel Gorman <mgorman@suse.de>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Michal Nazarewicz <mina86@mina86.com>, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, Christoph Lameter <cl@linux.com>, Rik van Riel <riel@redhat.com> Subject: Re: [PATCH 01/10] mm, compaction: do not recheck suitable_migration_target under lock Date: Mon, 9 Jun 2014 16:41:36 -0700 (PDT) [thread overview] Message-ID: <alpine.DEB.2.02.1406091636190.17705@chino.kir.corp.google.com> (raw) In-Reply-To: <1402305982-6928-1-git-send-email-vbabka@suse.cz> On Mon, 9 Jun 2014, Vlastimil Babka wrote: > isolate_freepages_block() rechecks if the pageblock is suitable to be a target > for migration after it has taken the zone->lock. However, the check has been > optimized to occur only once per pageblock, and compact_checklock_irqsave() > might be dropping and reacquiring lock, which means somebody else might have > changed the pageblock's migratetype meanwhile. > > Furthermore, nothing prevents the migratetype to change right after > isolate_freepages_block() has finished isolating. Given how imperfect this is, > it's simpler to just rely on the check done in isolate_freepages() without > lock, and not pretend that the recheck under lock guarantees anything. It is > just a heuristic after all. > > Signed-off-by: Vlastimil Babka <vbabka@suse.cz> > Cc: Minchan Kim <minchan@kernel.org> > Cc: Mel Gorman <mgorman@suse.de> > Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> > Cc: Michal Nazarewicz <mina86@mina86.com> > Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > Cc: Christoph Lameter <cl@linux.com> > Cc: Rik van Riel <riel@redhat.com> > Cc: David Rientjes <rientjes@google.com> Acked-by: David Rientjes <rientjes@google.com> We already do a preliminary check for suitable_migration_target() in isolate_freepages() in a racy way to avoid unnecessary work (and page_order() there is unprotected, I think you already mentioned this) so this seems fine to abandon. > --- > I suggest folding mm-compactionc-isolate_freepages_block-small-tuneup.patch into this > Hmm, Andrew was just moving some code around in that patch, I'm not sure that it makes sense to couple these two together and your patch here is addressing an optimization rather than a cleanup (and you've documented it well, no need to obscure it with unrelated changes). -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2014-06-09 23:41 UTC|newest] Thread overview: 88+ messages / expand[flat|nested] mbox.gz Atom feed top 2014-06-09 9:26 [PATCH 01/10] mm, compaction: do not recheck suitable_migration_target under lock Vlastimil Babka 2014-06-09 9:26 ` Vlastimil Babka 2014-06-09 9:26 ` [PATCH 02/10] mm, compaction: report compaction as contended only due to lock contention Vlastimil Babka 2014-06-09 9:26 ` Vlastimil Babka 2014-06-09 23:50 ` David Rientjes 2014-06-09 23:50 ` David Rientjes 2014-06-10 7:11 ` Vlastimil Babka 2014-06-10 7:11 ` Vlastimil Babka 2014-06-10 23:40 ` David Rientjes 2014-06-10 23:40 ` David Rientjes 2014-06-11 1:10 ` Minchan Kim 2014-06-11 1:10 ` Minchan Kim 2014-06-11 12:22 ` Vlastimil Babka 2014-06-11 12:22 ` Vlastimil Babka 2014-06-11 23:49 ` Minchan Kim 2014-06-11 23:49 ` Minchan Kim 2014-06-12 14:02 ` Vlastimil Babka 2014-06-12 14:02 ` Vlastimil Babka 2014-06-13 2:40 ` Minchan Kim 2014-06-13 2:40 ` Minchan Kim 2014-06-20 11:47 ` Vlastimil Babka 2014-06-20 11:47 ` Vlastimil Babka 2014-06-09 9:26 ` [PATCH 03/10] mm, compaction: periodically drop lock and restore IRQs in scanners Vlastimil Babka 2014-06-09 9:26 ` Vlastimil Babka 2014-06-09 23:58 ` David Rientjes 2014-06-09 23:58 ` David Rientjes 2014-06-10 7:15 ` Vlastimil Babka 2014-06-10 7:15 ` Vlastimil Babka 2014-06-10 23:41 ` David Rientjes 2014-06-10 23:41 ` David Rientjes 2014-06-11 1:32 ` Minchan Kim 2014-06-11 1:32 ` Minchan Kim 2014-06-11 11:24 ` Vlastimil Babka 2014-06-11 11:24 ` Vlastimil Babka 2014-06-09 9:26 ` [PATCH 04/10] mm, compaction: skip rechecks when lock was already held Vlastimil Babka 2014-06-09 9:26 ` Vlastimil Babka 2014-06-10 0:00 ` David Rientjes 2014-06-10 0:00 ` David Rientjes 2014-06-11 1:50 ` Minchan Kim 2014-06-11 1:50 ` Minchan Kim 2014-06-09 9:26 ` [PATCH 05/10] mm, compaction: remember position within pageblock in free pages scanner Vlastimil Babka 2014-06-09 9:26 ` Vlastimil Babka 2014-06-10 0:07 ` David Rientjes 2014-06-10 0:07 ` David Rientjes 2014-06-11 2:12 ` Minchan Kim 2014-06-11 2:12 ` Minchan Kim 2014-06-11 8:16 ` Joonsoo Kim 2014-06-11 8:16 ` Joonsoo Kim 2014-06-11 11:41 ` Vlastimil Babka 2014-06-11 11:41 ` Vlastimil Babka 2014-06-11 11:33 ` Vlastimil Babka 2014-06-11 11:33 ` Vlastimil Babka 2014-06-11 3:29 ` Zhang Yanfei 2014-06-11 3:29 ` Zhang Yanfei 2014-06-09 9:26 ` [PATCH 06/10] mm, compaction: skip buddy pages by their order in the migrate scanner Vlastimil Babka 2014-06-09 9:26 ` Vlastimil Babka 2014-06-10 0:08 ` David Rientjes 2014-06-10 0:08 ` David Rientjes 2014-06-09 9:26 ` [PATCH 07/10] mm: rename allocflags_to_migratetype for clarity Vlastimil Babka 2014-06-09 9:26 ` Vlastimil Babka 2014-06-11 2:41 ` Minchan Kim 2014-06-11 2:41 ` Minchan Kim 2014-06-11 3:38 ` Zhang Yanfei 2014-06-11 3:38 ` Zhang Yanfei 2014-06-09 9:26 ` [PATCH 08/10] mm, compaction: pass gfp mask to compact_control Vlastimil Babka 2014-06-09 9:26 ` Vlastimil Babka 2014-06-11 2:48 ` Minchan Kim 2014-06-11 2:48 ` Minchan Kim 2014-06-11 11:46 ` Vlastimil Babka 2014-06-11 11:46 ` Vlastimil Babka 2014-06-12 0:24 ` David Rientjes 2014-06-12 0:24 ` David Rientjes 2014-06-09 9:26 ` [RFC PATCH 09/10] mm, compaction: try to capture the just-created high-order freepage Vlastimil Babka 2014-06-09 9:26 ` Vlastimil Babka 2014-06-11 14:56 ` Vlastimil Babka 2014-06-11 14:56 ` Vlastimil Babka 2014-06-12 2:20 ` Minchan Kim 2014-06-12 2:20 ` Minchan Kim 2014-06-12 8:21 ` Vlastimil Babka 2014-06-12 8:21 ` Vlastimil Babka 2014-06-09 9:26 ` [RFC PATCH 10/10] mm, compaction: do not migrate pages when that cannot satisfy page fault allocation Vlastimil Babka 2014-06-09 9:26 ` Vlastimil Babka 2014-06-09 23:41 ` David Rientjes [this message] 2014-06-09 23:41 ` [PATCH 01/10] mm, compaction: do not recheck suitable_migration_target under lock David Rientjes 2014-06-11 0:33 ` Minchan Kim 2014-06-11 0:33 ` Minchan Kim 2014-06-11 2:45 ` Zhang Yanfei 2014-06-11 2:45 ` Zhang Yanfei
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