linux-kernel - Re: [PATCH] VM: kswapd should not do blocking memory allocations

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Message-ID: <1282306628.3927.0.camel@heimdal.trondhjem.org>
Date:	Fri, 20 Aug 2010 08:17:08 -0400
From:	Trond Myklebust <Trond.Myklebust@...app.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Ram Pai <ram.n.pai@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: Re: [PATCH] VM: kswapd should not do blocking memory allocations

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
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