linux-kernel - Re: [PATCH 0/4] 2.6.21-rc7 NFS writes: fix a series of issues

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Date:	Tue, 17 Apr 2007 22:14:02 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Florin Iucha <florin@...ha.net>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Adrian Bunk <bunk@...sta.de>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] 2.6.21-rc7 NFS writes: fix a series of issues

On Tue, 17 Apr 2007, Florin Iucha wrote:
> 
> Already did.  Traces from vanilla kernel at
>    http://iucha.net/nfs/21-rc7/big-copy

Well, there's a pdflush in io_schedule_timeout/congestion_wait, and 
there's a nfsv4-scv in svc_recv/nfs_callback_sv, and a lot of processes 
either just in schedule_timeout or similar "normal" waiting (pollwait 
etc).

[ The call traces could be prettier, but sadly, even if you enable frame 
  pointers, the x86-64 kernel is too stupid to follow them. So you kind of 
  just have to ignore the noise) ]

The triggering process looks like it might be that "cp", it is in the 
__wait_on_bit/sync_page/wait_on_page_bit/wait_on_page_writeback_range/ 
filemap_fdatawait.

Is this a trace from the "big copy" hang, or from a gnome splashscreen 
hang? It *looks* like it's a big copy. Yes/no?

Anyway, looks like the cp did a "utimes()" system call, which triggers 
"nfs_setattr(), which in turn triggers the filemap_fdatawait() and some 
kind of endless wait. Nothing stands out from the traces, in other words. 
Doesn't look like a locking thing, for example - we're not stuck on some 
inode semaphore, we're literally waiting for the page to be written out.

		Linus
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