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From: Vlastimil Babka <vbabka@suse.cz>
To: David Rientjes <rientjes@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	mgorman@techsingularity.net, Michal Hocko <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, Linux-MM layout <linux-mm@kvack.org>
Subject: Re: [LKP] [mm] ac5b2c1891: vm-scalability.throughput -61.3% regression
Date: Fri, 14 Dec 2018 22:33:42 +0100
Message-ID: <0700f5c3-66a8-338a-0ba0-2231cc3bb637@suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.21.1812141244450.186427@chino.kir.corp.google.com>

On 12/14/18 10:04 PM, David Rientjes wrote:
> On Wed, 12 Dec 2018, Vlastimil Babka wrote:

...

> Reclaim likely could be deterministically useful if we consider a redesign 
> of how migration sources and targets are determined in compaction.
> 
> Has anybody tried a migration scanner that isn't linearly based, rather 
> finding the highest-order free page of the same migratetype, iterating the 
> pages of its pageblock, and using this to determine whether the actual 
> migration will be worthwhile or not?

Not exactly that AFAIK, but a year ago in my series [1] patch 6 made
migration scanner 'prescan' the block of requested order before actually
trying to isolate anything for migration.

> I could imagine pageblock_skip being 
> repurposed for this as the heuristic.
> 
> Finding migration targets would be more tricky, but if we iterate the 
> pages of the pageblock for low-order free pages and find them to be mostly 
> used, that seems more appropriate than just pushing all memory to the end 
> of the zone?

Agree. That was patch 8/8 of the same series [1].

> It would be interesting to know if anybody has tried using the per-zone 
> free_area's to determine migration targets and set a bit if it should be 
> considered a migration source or a migration target.  If all pages for a 
> pageblock are not on free_areas, they are fully used.

Repurposing/adding a new pageblock bit was in my mind to help multiple
compactors not undo each other's work in the scheme where there's no
free page scanner, but I didn't implement it yet.

>>> otherwise we fail and defer because it wasn't able 
>>> to make a hugepage available.
>>
>> Note that THP fault compaction doesn't actually defer itself, which I
>> think is a weakness of the current implementation and hope that patch 3
>> in my series from yesterday [1] can address that. Because defering is
>> the general feedback mechanism that we have for suppressing compaction
>> (and thus associated reclaim) in cases it fails for any reason, not just
>> the one you mention. Instead of inspecting failure conditions in detail,
>> which would be costly, it's a simple statistical approach. And when
>> compaction is improved to fail less, defering automatically also happens
>> less.
>>
> 
> I couldn't get the link to work, unfortunately, I don't think the patch 
> series made it to LKML :/  I do see it archived for linux-mm, though, so 
> I'll take a look, thanks!

Yeah I forgot to Cc: LKML, but you were also in direct To: so you should
have received them directly. Also the abovementioned series, but that's
year ago. My fault for not returning to it after being done with the
Meltdown fun. I hope to do that soon.

[1] https://marc.info/?l=linux-mm&m=151315560308753

>> [1] https://lkml.kernel.org/r/20181211142941.20500-1-vbabka@suse.cz
>>


  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 [this message]
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
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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