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From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: Andrew Morton <akpm@osdl.org>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] nfs: fix congestion control
Date: Wed, 17 Jan 2007 09:49:58 +0100	[thread overview]
Message-ID: <1169023798.22935.96.camel@twins> (raw)
In-Reply-To: <1169014515.6065.5.camel@lade.trondhjem.org>

On Wed, 2007-01-17 at 01:15 -0500, Trond Myklebust wrote:
> On Wed, 2007-01-17 at 03:41 +0100, Peter Zijlstra wrote:
> > On Tue, 2007-01-16 at 17:27 -0500, Trond Myklebust wrote:
> > > On Tue, 2007-01-16 at 23:08 +0100, Peter Zijlstra wrote:
> > > > Subject: nfs: fix congestion control
> > > > 
> > > > The current NFS client congestion logic is severely broken, it marks the
> > > > backing device congested during each nfs_writepages() call and implements
> > > > its own waitqueue.
> > > > 
> > > > Replace this by a more regular congestion implementation that puts a cap
> > > > on the number of active writeback pages and uses the bdi congestion waitqueue.
> > > > 
> > > > NFSv[34] commit pages are allowed to go unchecked as long as we are under 
> > > > the dirty page limit and not in direct reclaim.
> > 
> > > 
> > > What on earth is the point of adding congestion control to COMMIT?
> > > Strongly NACKed.
> > 
> > They are dirty pages, how are we getting rid of them when we reached the
> > dirty limit?
> 
> They are certainly _not_ dirty pages. They are pages that have been
> written to the server but are not yet guaranteed to have hit the disk
> (they were only written to the server's page cache). We don't care if
> they are paged in or swapped out on the local client.
> 
> \All the COMMIT does, is to ask the server to write the data from its
> page cache onto disk. Once that has been done, we can release the pages.
> If the commit fails, then we iterate through the whole writepage()
> process again. The commit itself does, however, not even look at the
> page data.

Thou art correct from an NFS point of view, however for the VM they are
(still) just dirty pages and we need shed them.

You talk of swapping them out, they are filecache pages not swapcache
pages. The writepage() process needs to complete and that entails
committing them.

> > > Why 16MB of on-the-wire data? Why not 32, or 128, or ...
> > 
> > Andrew always promotes a fixed number for congestion control, I pulled
> > one from a dark place. I have no problem with a more dynamic solution.
> > 
> > > Solaris already allows you to send 2MB of write data in a single RPC
> > > request, and the RPC engine has for some time allowed you to tune the
> > > number of simultaneous RPC requests you have on the wire: Chuck has
> > > already shown that read/write performance is greatly improved by upping
> > > that value to 64 or more in the case of RPC over TCP. Why are we then
> > > suddenly telling people that they are limited to 8 simultaneous writes?
> > 
> > min(max RPC size * max concurrent RPC reqs, dirty threshold) then?
> 
> That would be far preferable. For instance, it allows those who have
> long latency fat pipes to actually use the bandwidth optimally when
> writing out the data.

I will make it so then ;-)

I found max concurrent RPCs to be xprt_{tcp,udp}_slot_table_entries(?),
where might I find the max RPC size? 

(Any pointer to just RTFM are equally well received)


  reply	other threads:[~2007-01-17  8:52 UTC|newest]

Thread overview: 110+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-16  5:47 [RFC 0/8] Cpuset aware writeback 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 [this message]
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   ` [RFC 0/8] Cpuset aware writeback Christoph Lameter
2007-01-16 23:40     ` 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

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