linux-kernel - Re: [PATCH 0/2] tmpfs: Improve tmpfs scalability

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Message-ID: <alpine.DEB.1.00.1005201837040.21050@tigran.mtv.corp.google.com>
Date:	Thu, 20 May 2010 18:55:15 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	tim <tim.c.chen@...ux.intel.com>
cc:	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/2] tmpfs: Improve tmpfs scalability

On Tue, 18 May 2010, tim wrote:
> 
> We created a token jar library implementing
> per cpu cache of tokens to avoid lock contentions whenever
> we retrieve or return a token to a token jar.  Using this library
> with tmpfs, we find Aim7 fserver throughput improved 270% 
> on a 4 socket, 32 cores NHM-EX system.
> 
> In current implementation of tmpfs, whenever we
> get a new page, stat_lock in shmem_sb_info needs to be acquired.  
> This causes a lot of lock contentions when multiple
> threads are using tmpfs simultaneously, which makes
> system with large number of cpus scale poorly.
> Almost 75% of cpu time was spent contending on
> stat_lock when we ran Aim7 fserver load with 128 threads
> on a 4 socket, 32 cores NHM-EX system.
> 
> The first patch in the series implements the quick token jar. 
> The second patch update the shmem code of tmpfs to use this
> library to improve tmpfs performance.

Interesting, thank you - I'll take a look, but not this week.

I do hope you're using Aim7 just as an example: you know that mounting
tmpfs with nr_blocks=0,nr_inodes=0 skips those shmem_sb_info updates
altogether?  Mounting in such a way should be fine for getting better
numbers out of Aim7; but yes, there are reallife uses for tmpfs which
are safer with the nr_blocks,nr_inodes limits.

Hugh
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