LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Christoph Lameter <clameter@sgi.com>
To: Andrew Morton <akpm@osdl.org>
Cc: menage@google.com, linux-kernel@vger.kernel.org,
	nickpiggin@yahoo.com.au, linux-mm@kvack.org, ak@suse.de,
	pj@sgi.com, dgc@sgi.com
Subject: Re: [RFC 0/8] Cpuset aware writeback
Date: Tue, 16 Jan 2007 14:15:56 -0800 (PST)	[thread overview]
Message-ID: <Pine.LNX.4.64.0701161407530.3545@schroedinger.engr.sgi.com> (raw)
In-Reply-To: <20070116135325.3441f62b.akpm@osdl.org>

On Tue, 16 Jan 2007, Andrew Morton wrote:

> > On Mon, 15 Jan 2007 21:47:43 -0800 (PST) Christoph Lameter <clameter@sgi.com> wrote:
> >
> > Currently cpusets are not able to do proper writeback since
> > dirty ratio calculations and writeback are all done for the system
> > as a whole.
> 
> We _do_ do proper writeback.  But it's less efficient than it might be, and
> there's an NFS problem.

Well yes we write back during LRU scans when a potentially high percentage 
of the memory in cpuset is dirty.

> > This may result in a large percentage of a cpuset
> > to become dirty without writeout being triggered. Under NFS
> > this can lead to OOM conditions.
> 
> OK, a big question: is this patchset a performance improvement or a
> correctness fix?  Given the above, and the lack of benchmark results I'm
> assuming it's for correctness.

It is a correctness fix both for NFS OOM and doing proper cpuset writeout.

> - Why does NFS go oom?  Because it allocates potentially-unbounded
>   numbers of requests in the writeback path?
> 
>   It was able to go oom on non-numa machines before dirty-page-tracking
>   went in.  So a general problem has now become specific to some NUMA
>   setups.


Right. The issue is that large portions of memory become dirty / 
writeback since no writeback occurs because dirty limits are not checked 
for a cpuset. Then NFS attempt to writeout when doing LRU scans but is 
unable to allocate memory.
 
>   So an obvious, equivalent and vastly simpler "fix" would be to teach
>   the NFS client to go off-cpuset when trying to allocate these requests.

Yes we can fix these allocations by allowing processes to allocate from 
other nodes. But then the container function of cpusets is no longer 
there.

> (But is it really bad? What actual problems will it cause once NFS is fixed?)

NFS is okay as far as I can tell. dirty throttling works fine in non 
cpuset environments because we throttle if 40% of memory becomes dirty or 
under writeback.

> I don't understand why the proposed patches are cpuset-aware at all.  This
> is a per-zone problem, and a per-zone fix would seem to be appropriate, and
> more general.  For example, i386 machines can presumably get into trouble
> if all of ZONE_DMA or ZONE_NORMAL get dirty.  A good implementation would
> address that problem as well.  So I think it should all be per-zone?

No. A zone can be completely dirty as long as we are allowed to allocate 
from other zones.

> Do we really need those per-inode cpumasks?  When page reclaim encounters a
> dirty page on the zone LRU, we automatically know that page->mapping->host
> has at least one dirty page in this zone, yes?  We could immediately ask

Yes, but when we enter reclaim most of the pages of a zone may already be 
dirty/writeback so we fail. Also when we enter reclaim we may not have
the proper process / cpuset context. There is no use to throttle kswapd. 
We need to throttle the process that is dirtying memory.

> But all of this is, I think, unneeded if NFS is fixed.  It's hopefully a
> performance optimisation to permit writeout in a less seeky fashion. 
> Unless there's some other problem with excessively dirty zones.

The patchset improves performance because the filesystem can do sequential 
writeouts. So yes in some ways this is a performance improvement. But this 
is only because this patch makes dirty throttling for cpusets work in the 
same way as for non NUMA system.

  parent reply	other threads:[~2007-01-16 22:16 UTC|newest]

Thread overview: 110+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-16  5:47 Christoph Lameter
2007-01-16  5:47 ` [RFC 1/8] Convert higest_possible_node_id() into nr_node_ids Christoph Lameter
2007-01-16 22:05   ` Andi Kleen
2007-01-17  3:14     ` Christoph Lameter
2007-01-17  4:15       ` Andi Kleen
2007-01-17  4:23         ` Christoph Lameter
2007-01-16  5:47 ` [RFC 2/8] Add a map to inodes to track dirty pages per node Christoph Lameter
2007-01-16  5:47 ` [RFC 3/8] Add a nodemask to pdflush functions Christoph Lameter
2007-01-16  5:48 ` [RFC 4/8] Per cpuset dirty ratio handling and writeout Christoph Lameter
2007-01-16  5:48 ` [RFC 5/8] Make writeout during reclaim cpuset aware Christoph Lameter
2007-01-16 22:07   ` Andi Kleen
2007-01-17  4:20     ` Paul Jackson
2007-01-17  4:28       ` Andi Kleen
2007-01-17  4:36         ` Paul Jackson
2007-01-17  5:59           ` Andi Kleen
2007-01-17  6:19             ` Christoph Lameter
2007-01-17  4:23     ` Christoph Lameter
2007-01-16  5:48 ` [RFC 6/8] Throttle vm writeout per cpuset Christoph Lameter
2007-01-16  5:48 ` [RFC 7/8] Exclude unreclaimable pages from dirty ration calculation Christoph Lameter
2007-01-18 15:48   ` Nikita Danilov
2007-01-18 19:56     ` Christoph Lameter
2007-01-16  5:48 ` [RFC 8/8] Reduce inode memory usage for systems with a high MAX_NUMNODES Christoph Lameter
2007-01-16 19:52   ` Paul Menage
2007-01-16 20:00     ` Christoph Lameter
2007-01-16 20:06       ` Paul Menage
2007-01-16 20:51         ` Christoph Lameter
2007-01-16  7:38 ` [RFC 0/8] Cpuset aware writeback Peter Zijlstra
2007-01-16 20:10   ` Christoph Lameter
2007-01-16  9:25 ` Paul Jackson
2007-01-16 17:13   ` Christoph Lameter
2007-01-16 21:53 ` Andrew Morton
2007-01-16 22:08   ` [PATCH] nfs: fix congestion control Peter Zijlstra
2007-01-16 22:27     ` Trond Myklebust
2007-01-17  2:41       ` Peter Zijlstra
2007-01-17  6:15         ` Trond Myklebust
2007-01-17  8:49           ` Peter Zijlstra
2007-01-17 13:50             ` Trond Myklebust
2007-01-17 14:29               ` Peter Zijlstra
2007-01-17 14:45                 ` Trond Myklebust
2007-01-17 20:05     ` Christoph Lameter
2007-01-17 21:52       ` Peter Zijlstra
2007-01-17 21:54         ` Trond Myklebust
2007-01-18 13:27           ` Peter Zijlstra
2007-01-18 15:49             ` Trond Myklebust
2007-01-19  9:33               ` Peter Zijlstra
2007-01-19 13:07                 ` Peter Zijlstra
2007-01-19 16:51                   ` Trond Myklebust
2007-01-19 17:54                     ` Peter Zijlstra
2007-01-19 17:20                   ` Christoph Lameter
2007-01-19 17:57                     ` Peter Zijlstra
2007-01-19 18:02                       ` Christoph Lameter
2007-01-19 18:26                       ` Trond Myklebust
2007-01-19 18:27                         ` Christoph Lameter
2007-01-20  7:01                         ` [PATCH] nfs: fix congestion control -v3 Peter Zijlstra
2007-01-22 16:12                           ` Trond Myklebust
2007-01-25 15:32                             ` [PATCH] nfs: fix congestion control -v4 Peter Zijlstra
2007-01-26  5:02                               ` Andrew Morton
2007-01-26  8:00                                 ` Peter Zijlstra
2007-01-26  8:50                                   ` Peter Zijlstra
2007-01-26  5:09                               ` Andrew Morton
2007-01-26  5:31                                 ` Christoph Lameter
2007-01-26  6:04                                   ` Andrew Morton
2007-01-26  6:53                                     ` Christoph Lameter
2007-01-26  8:03                                     ` Peter Zijlstra
2007-01-26  8:51                                       ` Andrew Morton
2007-01-26  9:01                                         ` Peter Zijlstra
2007-02-20 12:59                                         ` Peter Zijlstra
2007-01-22 17:59                           ` [PATCH] nfs: fix congestion control -v3 Christoph Lameter
2007-01-17 23:15     ` [PATCH] nfs: fix congestion control Christoph Hellwig
2007-01-16 22:15   ` Christoph Lameter [this message]
2007-01-16 23:40     ` [RFC 0/8] Cpuset aware writeback Andrew Morton
2007-01-17  0:16       ` Christoph Lameter
2007-01-17  1:07         ` Andrew Morton
2007-01-17  1:30           ` Christoph Lameter
2007-01-17  2:34             ` Andrew Morton
2007-01-17  3:40               ` Christoph Lameter
2007-01-17  4:02                 ` Paul Jackson
2007-01-17  4:05                 ` Andrew Morton
2007-01-17  6:27                   ` Christoph Lameter
2007-01-17  7:00                     ` Andrew Morton
2007-01-17  8:01                       ` Paul Jackson
2007-01-17  9:57                         ` Andrew Morton
2007-01-17 19:43                       ` Christoph Lameter
2007-01-17 22:10                         ` Andrew Morton
2007-01-18  1:10                           ` Christoph Lameter
2007-01-18  1:25                             ` Andrew Morton
2007-01-18  5:21                               ` Christoph Lameter
2007-01-16 23:44   ` David Chinner
2007-01-16 22:01 ` Andi Kleen
2007-01-16 22:18   ` Christoph Lameter
2007-02-02  1:38 ` Ethan Solomita
2007-02-02  2:16   ` Christoph Lameter
2007-02-02  4:03     ` Andrew Morton
2007-02-02  5:29       ` Christoph Lameter
2007-02-02  6:02         ` Neil Brown
2007-02-02  6:17           ` Christoph Lameter
2007-02-02  6:41             ` Neil Brown
2007-02-02  7:12         ` Andrew Morton
2007-03-21 21:11     ` Ethan Solomita
2007-03-21 21:29       ` Christoph Lameter
2007-03-21 21:52         ` Andrew Morton
2007-03-21 21:57           ` Christoph Lameter
2007-04-19  2:07         ` Ethan Solomita
2007-04-19  2:55           ` Christoph Lameter
2007-04-19  7:52             ` Ethan Solomita
2007-04-19 16:03               ` Christoph Lameter
2007-04-21  1:37             ` Ethan Solomita
2007-04-21  1:48               ` Christoph Lameter
2007-04-21  8:15                 ` Ethan Solomita
2007-04-21 15:40                   ` Christoph Lameter

Reply instructions:

You may reply publicly 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=Pine.LNX.4.64.0701161407530.3545@schroedinger.engr.sgi.com \
    --to=clameter@sgi.com \
    --cc=ak@suse.de \
    --cc=akpm@osdl.org \
    --cc=dgc@sgi.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=menage@google.com \
    --cc=nickpiggin@yahoo.com.au \
    --cc=pj@sgi.com \
    --subject='Re: [RFC 0/8] Cpuset aware writeback' \
    /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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).