netdev - Re: SOCK_MEMALLOC vs loopback

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Message-ID: <20150305095044.GR3087@suse.de>
Date:	Thu, 5 Mar 2015 09:50:44 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Mike Christie <mchristi@...hat.com>
Cc:	Ilya Dryomov <idryomov@...il.com>, ceph-devel@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>,
	Sage Weil <sage@...hat.com>, NeilBrown <neilb@...e.de>,
	netdev@...r.kernel.org
Subject: Re: SOCK_MEMALLOC vs loopback

On Wed, Mar 04, 2015 at 10:03:51PM -0600, Mike Christie wrote:
> On 03/04/2015 02:04 PM, Mel Gorman wrote:
> > other options. If that contract is not met then using it can deadlock the
> > system. It's the same for PF_MEMALLOC -- activating that is a recipe for
> > deadlock due to memory exhaustion.
> 
> For rbd and iscsi's SOCK_MEMALLOC/PF_MEMALLOC use, I copied what you did
> for nbd in commit 7f338fe4540b1d0600b02314c7d885fd358e9eca which always
> sets those flags and seems to rely on the network layer to do the right
> thing. Are they all incorrect?

NBD is a poor example and if it comes to that, I would suggest removing it
and let NBD easily deadlock like it used to. NBD has other failure cases
such as the client can get paged out if -swap is not specified. The same
commit notes that NBD may still deadlock and that min_free_kbytes may have
to be increased.

-- 
Mel Gorman
SUSE Labs
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