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From: Trond Myklebust <Trond.Myklebust@netapp.com>
To: Chuck Lever <chuck.lever@oracle.com>
Cc: linux-nfs@vger.kernel.org
Subject: Re: [PATCH] NFS: Use GFP_NOFS in nfs_direct_req_alloc
Date: Tue, 08 Sep 2009 23:49:53 -0400	[thread overview]
Message-ID: <1252468193.5092.29.camel@heimdal.trondhjem.org> (raw)
In-Reply-To: <CDD6BAFB-F9E3-4724-893E-94589560E8BF@oracle.com>

On Tue, 2009-09-08 at 22:16 -0400, Chuck Lever wrote:
> On Sep 8, 2009, at 9:37 PM, Trond Myklebust wrote:
> > On Tue, 2009-09-08 at 21:01 -0400, Chuck Lever wrote:
> >> That is precisely the case here, in fact.  The upper file system is
> >> attempting to reclaim memory in the same kernel where the NFS client
> >> is trying to allocate with GFP_KERNEL.
> >
> > That's the "upper file system"'s problem, not ours... Stacking
> > filesystems causes issues. Screwing over the existing users of the
> > underlying filesystem is not a fix for those issues...
> 
> How does this change "screw over" the existing users of NFS O_DIRECT?

If they are low on memory, and call read() or write() on an O_DIRECT
file, the kernel will fail to start the necessary memory reclaim. Given
that by far the most common users of NFS O_DIRECT these days tend to be
large databases with rather heavy memory requirements our code changes
should rather be moving in the opposite direction w.r.t. use of
GFP_NOFS.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com

      reply	other threads:[~2009-09-09  3:50 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-09-08 22:05 [PATCH] NFS: Use GFP_NOFS in nfs_direct_req_alloc Chuck Lever
     [not found] ` <20090908220230.7590.69833.stgit-RytpoXr2tKZ9HhUboXbp9zCvJB+x5qRC@public.gmane.org>
2009-09-08 22:32   ` Trond Myklebust
     [not found]     ` <1252449178.8099.64.camel-rJ7iovZKK19ZJLDQqaL3InhyD016LWXt@public.gmane.org>
2009-09-08 22:43       ` Chuck Lever
2009-09-08 23:05         ` Trond Myklebust
     [not found]           ` <1252451130.8099.81.camel-rJ7iovZKK19ZJLDQqaL3InhyD016LWXt@public.gmane.org>
2009-09-09  1:01             ` Chuck Lever
2009-09-09  1:37               ` Trond Myklebust
     [not found]                 ` <1252460233.5092.12.camel-rJ7iovZKK19ZJLDQqaL3InhyD016LWXt@public.gmane.org>
2009-09-09  2:16                   ` Chuck Lever
2009-09-09  3:49                     ` Trond Myklebust [this message]

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