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From: Vlastimil Babka <vbabka@suse.cz>
To: Andrea Arcangeli <aarcange@redhat.com>,
	David Rientjes <rientjes@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	mgorman@techsingularity.net, mhocko@kernel.org,
	ying.huang@intel.com, s.priebe@profihost.ag,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	alex.williamson@redhat.com, lkp@01.org, kirill@shutemov.name,
	Andrew Morton <akpm@linux-foundation.org>,
	zi.yan@cs.rutgers.edu
Subject: Re: [LKP] [mm] ac5b2c1891: vm-scalability.throughput -61.3% regression
Date: Thu, 6 Dec 2018 10:23:15 +0100
Message-ID: <a55a4fe9-6abe-ccb8-befd-afdacac2829d@suse.cz> (raw)
In-Reply-To: <20181206005425.GB21159@redhat.com>

On 12/6/18 1:54 AM, Andrea Arcangeli wrote:
> On Wed, Dec 05, 2018 at 04:18:14PM -0800, David Rientjes wrote:
>> On Wed, 5 Dec 2018, Andrea Arcangeli wrote:
>>
>> Note that in addition to COMPACT_SKIPPED that you mention, compaction can 
>> fail with COMPACT_COMPLETE, meaning the full scan has finished without 
>> freeing a hugepage, or COMPACT_DEFERRED, meaning that doing another scan 
>> is unlikely to produce a different result.  COMPACT_SKIPPED makes sense to 
>> do reclaim if it can become accessible to isolate_freepages() and 
>> hopefully another allocator does not allocate from these newly freed pages 
>> before compaction can scan the zone again.  For COMPACT_COMPLETE and 
>> COMPACT_DEFERRED, reclaim is unlikely to ever help.
> 
> The COMPACT_COMPLETE and (COMPACT_PARTIAL_SKIPPED for that matter)
> seems just a mistake in the max() evaluation try_to_compact_pages()
> that let it return COMPACT_COMPLETE and COMPACT_PARTIAL_SKIPPED. I
> think it should just return COMPACT_DEFERRED in those two cases and it
> should be enforced forced for all prio.
> 
> There are really only 3 cases that matter for the caller:
> 
> 1) succeed -> we got the page
> 2) defer -> we failed (caller won't care about why)
> 3) skipped -> failed because not enough 4k freed -> reclaim must be invoked then
>    compaction can be retried
> 
> PARTIAL_SKIPPED/COMPLETE both fall into 2) above so for the caller
> they should be treated the same way. It doesn't seem very concerning
> that it may try like if it succeeded and do a spurious single reclaim
> invocation, but it's good to fix this and take the COMPACT_DEFERRED
> nopage path in the __GFP_NORETRY case.

Yeah good point. I wouldn't change the general logic of
try_to_compact_pages() though, but the condition for __GFP_NORETRY can
simply change to:

if (compact_result != COMPACT_SKIPPED)
     goto nopage;

I can make a patch ASAP together with a few others I think are needed,
that should hopefully avoid the need for __GFP_COMPACT_ONLY or checks
based on order. What's probably unavoidable though is adding back
__GFP_NORETRY for madvised allocations (i.e. partially reverting
2516035499b95), but David was fine with that and your __GFP_ONLY_COMPACT
approach effectively did it too.


  reply index

Thread overview: 77+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-27  6:25 kernel test robot
2018-11-27 17:08 ` Linus Torvalds
2018-11-27 18:17   ` Michal Hocko
2018-11-27 18:21     ` Michal Hocko
2018-11-27 19:05   ` Vlastimil Babka
2018-11-27 19:16     ` Vlastimil Babka
2018-11-27 20:57   ` Andrea Arcangeli
2018-11-27 22:50     ` Linus Torvalds
2018-11-28  6:30       ` Michal Hocko
2018-11-28  3:20     ` Huang\, Ying
2018-11-28 16:48       ` Linus Torvalds
2018-11-28 18:39         ` Andrea Arcangeli
2018-11-28 23:10         ` David Rientjes
2018-12-03 18:01         ` Linus Torvalds
2018-12-03 18:14           ` Michal Hocko
2018-12-03 18:19             ` Linus Torvalds
2018-12-03 18:30               ` Michal Hocko
2018-12-03 18:45                 ` Linus Torvalds
2018-12-03 18:59                   ` Michal Hocko
2018-12-03 19:23                     ` Andrea Arcangeli
2018-12-03 20:26                       ` David Rientjes
2018-12-03 19:28                     ` Linus Torvalds
2018-12-03 20:12                       ` Andrea Arcangeli
2018-12-03 20:36                         ` David Rientjes
2018-12-03 22:04                         ` Linus Torvalds
2018-12-03 22:27                           ` Linus Torvalds
2018-12-03 22:57                             ` David Rientjes
2018-12-04  9:22                             ` Vlastimil Babka
2018-12-04 10:45                               ` Mel Gorman
2018-12-05  0:47                                 ` David Rientjes
2018-12-05  9:08                                   ` Michal Hocko
2018-12-05 10:43                                     ` Mel Gorman
2018-12-05 11:43                                       ` Michal Hocko
2018-12-05 10:06                                 ` Mel Gorman
2018-12-05 20:40                                 ` Andrea Arcangeli
2018-12-05 21:59                                   ` David Rientjes
2018-12-06  0:00                                     ` Andrea Arcangeli
2018-12-05 22:03                                   ` Linus Torvalds
2018-12-05 22:12                                     ` David Rientjes
2018-12-05 23:36                                     ` Andrea Arcangeli
2018-12-05 23:51                                       ` Linus Torvalds
2018-12-06  0:58                                         ` Linus Torvalds
2018-12-06  9:14                                           ` MADV_HUGEPAGE vs. NUMA semantic (was: Re: [LKP] [mm] ac5b2c1891: vm-scalability.throughput -61.3% regression) Michal Hocko
2018-12-06 23:49                                             ` David Rientjes
2018-12-07  7:34                                               ` Michal Hocko
2018-12-07  4:31                                             ` Linus Torvalds
2018-12-07  7:49                                               ` Michal Hocko
2018-12-07  9:06                                                 ` Vlastimil Babka
2018-12-07 23:15                                                   ` David Rientjes
2018-12-06 23:43                                           ` [LKP] [mm] ac5b2c1891: vm-scalability.throughput -61.3% regression David Rientjes
2018-12-07  4:01                                             ` Linus Torvalds
2018-12-10  0:29                                               ` David Rientjes
2018-12-10  4:49                                                 ` Andrea Arcangeli
2018-12-12  0:37                                                   ` David Rientjes
2018-12-12  9:50                                                     ` Michal Hocko
2018-12-12 17:00                                                       ` Andrea Arcangeli
2018-12-14 11:32                                                         ` Michal Hocko
2018-12-12 10:14                                                     ` Vlastimil Babka
2018-12-14 21:04                                                       ` David Rientjes
2018-12-14 21:33                                                         ` Vlastimil Babka
2018-12-21 22:18                                                           ` David Rientjes
2018-12-22 12:08                                                             ` Mel Gorman
2018-12-14 23:11                                                         ` Mel Gorman
2018-12-21 22:15                                                           ` David Rientjes
2018-12-12 10:44                                                   ` Andrea Arcangeli
2019-04-15 11:48                                             ` Michal Hocko
2018-12-06  0:18                                       ` David Rientjes
2018-12-06  0:54                                         ` Andrea Arcangeli
2018-12-06  9:23                                           ` Vlastimil Babka [this message]
2018-12-03 20:39                     ` David Rientjes
2018-12-03 21:25                       ` Michal Hocko
2018-12-03 21:53                         ` David Rientjes
2018-12-04  8:48                           ` Michal Hocko
2018-12-05  0:07                             ` David Rientjes
2018-12-05 10:18                               ` Michal Hocko
2018-12-05 19:16                                 ` David Rientjes
2018-11-27  7:23 kernel test robot

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