linux-kernel - Re: fs/stat: Reduce memory requirements for stat

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Message-ID: <20140612134149.GC4296@osiris>
Date:	Thu, 12 Jun 2014 15:41:49 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Stefan Bader <stefan.bader@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: fs/stat: Reduce memory requirements for stat_open

On Thu, Jun 12, 2014 at 03:00:17PM +0200, Stefan Bader wrote:
> When reading from /proc/stat we allocate a large buffer to maximise
> the chances of the results being from a single run and thus internally
> consistent.  This currently is sized at 128 * num_possible_cpus() which,
> in the face of kernels sized to handle large configurations (256 cpus
> plus), results in the buffer being an order-4 allocation or more.
> When system memory becomes fragmented these cannot be guarenteed, leading
> to read failures due to allocation failures.
> 
> There seem to be two issues in play here.  Firstly the allocation is
> going to be vastly over sized in the common case, as we only consume the
> buffer based on the num_online_cpus().  Secondly, regardless of size we
> should not be requiring allocations greater than PAGE_ALLOC_COSTLY_ORDER
> as allocations above this order are significantly more likely to fail.
> 
> The following patch addesses both of these issues.  Does that make sense
> generally? It seemed to stop top complaining wildly for the reporter
> at least.

Hi Stefan,

see also https://lkml.org/lkml/2014/5/21/341

and one possible solution:

https://lkml.org/lkml/2014/5/30/191

and the other one:

https://lkml.org/lkml/2014/6/12/92
https://lkml.org/lkml/2014/6/12/107

Thanks,
Heiko

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