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

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Date:	Fri, 20 Aug 2010 13:45:33 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Trond Myklebust <Trond.Myklebust@...app.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

> 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?

Thanks,
Fengguang

> 		nfs_commit_inode(mapping->host, how);
> 	}
> 
> Remove the 'if (current_is_kswapd())' line, and run an mmap() write
> intensive workload, and it should hang pretty much every time.
> 
> Cheers
>   Trond
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