LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Vlastimil Babka <vbabka@suse.cz>
To: David Rientjes <rientjes@google.com>,
	Andrea Arcangeli <aarcange@redhat.com>
Cc: 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
Subject: Re: [LKP] [mm] ac5b2c1891: vm-scalability.throughput -61.3% regression
Date: Wed, 12 Dec 2018 11:14:05 +0100
Message-ID: <0bbf4202-6187-28fb-37b7-da6885b89cce@suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.21.1812111609060.255489@chino.kir.corp.google.com>

On 12/12/18 1:37 AM, David Rientjes wrote:
> 
> Regarding the role of direct reclaim in the allocator, I think we need 
> work on the feedback from compaction to determine whether it's worthwhile.  
> That's difficult because of the point I continue to bring up: 
> isolate_freepages() is not necessarily always able to access this freed 
> memory.

That's one of the *many* reasons why having free base pages doesn't
guarantee compaction success. We can and will improve on that. But I
don't think it would be e.g. practical to check the pfns of free pages
wrt compaction scanner positions and decide based on that. Also when you
invoke reclaim, you can't tell in advance those pfns, so I'm not sure
how the better feedback from compaction to reclaim for this specific
aspect would be supposed to work?

> But for cases where we get COMPACT_SKIPPED because the order-0 
> watermarks are failing, reclaim *is* likely to have an impact in the 
> success of compaction,

Yes that's the heuristic we rely on.

> 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.

>  [ If we run compaction regardless of the order-0 watermark check and find
>    a pageblock where we can likely free a hugepage because it is 
>    fragmented movable pages, this is a pretty good indication that reclaim
>    is worthwhile iff the reclaimed memory is beyond the migration scanner. ]

I don't think that would be a good direction to pursue, to let scanning
happen even without having the free pages. Also as I've mentioned above,
LRU-based reclaim cannot satisfy your 'iff' condition, unless it
inspected the pfn's it freed, and continued reclaiming until enough of
those beyond migration scanner were freed. Instead IMHO we should look
again into replacing the free scanner with direct allocation from freelists.

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

  parent 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 [this message]
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
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

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=0bbf4202-6187-28fb-37b7-da6885b89cce@suse.cz \
    --to=vbabka@suse.cz \
    --cc=aarcange@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=alex.williamson@redhat.com \
    --cc=kirill@shutemov.name \
    --cc=linux-kernel@vger.kernel.org \
    --cc=lkp@01.org \
    --cc=mgorman@techsingularity.net \
    --cc=mhocko@kernel.org \
    --cc=rientjes@google.com \
    --cc=s.priebe@profihost.ag \
    --cc=torvalds@linux-foundation.org \
    --cc=ying.huang@intel.com \
    --cc=zi.yan@cs.rutgers.edu \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org linux-kernel@archiver.kernel.org
	public-inbox-index lkml


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/ public-inbox