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Subject: Re: [PATCH] VM: kswapd should not do blocking memory allocations
From: Trond Myklebust <Trond.Myklebust@netapp.com>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Ram Pai <ram.n.pai@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org
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Date: Fri, 20 Aug 2010 08:17:08 -0400
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On Fri, 2010-08-20 at 13:45 +0800, Wu Fengguang wrote:
> > Hi Ram,
> > 
> > I was seeing it on NFS until I put in the following kswapd-specific hack
> > into nfs_release_page():
> > 
> > 	/* Only do I/O if gfp is a superset of GFP_KERNEL */
> > 	if (mapping && (gfp & GFP_KERNEL) == GFP_KERNEL) {
> > 		int how = FLUSH_SYNC;
> > 
> > 		/* Don't let kswapd deadlock waiting for OOM RPC calls */
> > 		if (current_is_kswapd())
> > 			how = 0;
> 
> So the patch can remove the above workaround together, and add comment
> that NFS exploits the gfp mask to avoid complex operations involving
> recursive memory allocation and hence deadlock?

I thought I'd send that as a separate patch, but yes, that is my
intention next.

Cheers
  Trond