linux-kernel - Re: Deadlock in NFSv4 in all kernels

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Message-ID: <20100525140742.GM12852@horn.ics.muni.cz>
Date:	Tue, 25 May 2010 16:07:42 +0200
From:	Zdenek Salvet <salvet@....muni.cz>
To:	Trond Myklebust <trond.myklebust@....uio.no>
Cc:	Lukas Hejtmanek <xhejtman@....muni.cz>,
	Pavel Machek <pavel@....cz>, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	salvet@....muni.cz
Subject: Re: Deadlock in NFSv4 in all kernels

On Tue, May 25, 2010 at 09:39:25AM -0400, Trond Myklebust wrote:
> The schemes I'm talking about typically had special memory pools
> preallocated for use by daemons, and would label the daemons using some
> equivalent of the PF_MEMALLOC flag to prevent recursion into the
> filesystem.

Yes. In my opinion, proper solution has to be careful at three points:
- daemons must be carefully written not to require much memory
- daemons should 'inherit' PF_MEMALLOC while processing upcalls 
- FS should try to flush fast enough (what W. Adamson wrote) and 
  delay new allocations when it cannot 

Regards,

Zdenek Salvet                                              salvet@....muni.cz 
Institute of Computer Science of Masaryk University, Brno, Czech Republic
and CESNET, z.s.p.o., Prague, Czech Republic
Phone: ++420-549 49 6534                           Fax: ++420-541 212 747
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