linux-kernel - Re: [PATCH] net: use __GFP_NORETRY for high order allocations

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Message-ID: <87y51me9lr.fsf@xmission.com>
Date:	Fri, 07 Feb 2014 16:22:56 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org,
	rientjes@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: use __GFP_NORETRY for high order allocations

David Miller <davem@...emloft.net> writes:

> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Thu, 06 Feb 2014 10:42:42 -0800
>
>> From: Eric Dumazet <edumazet@...gle.com>
>> 
>> sock_alloc_send_pskb() & sk_page_frag_refill()
>> have a loop trying high order allocations to prepare
>> skb with low number of fragments as this increases performance.
>> 
>> Problem is that under memory pressure/fragmentation, this can
>> trigger OOM while the intent was only to try the high order
>> allocations, then fallback to order-0 allocations.
>> 
>> We had various reports from unexpected regressions.
>> 
>> According to David, setting __GFP_NORETRY should be fine,
>> as the asynchronous compaction is still enabled, and this
>> will prevent OOM from kicking as in :
>  ...
>> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>> Acked-by: David Rientjes <rientjes@...gle.com>
>
> Applied, do we want this for -stable?

The first hunk goes back to 3.12 and the second hunk goes back to 3.8.

I think so.    The change is safe and this class of problem can cause an
external attack to trigger an OOM on your box, by controlling the packet
flow.

Eric
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