linux-kernel - Re: [PATCH v2 1/2] Make the batch size of the percpu

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Message-Id: <20130529122605.082cbb1ad8f5cbc9e82e7b16@linux-foundation.org>
Date:	Wed, 29 May 2013 12:26:05 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Ric Mason <ric.masonn@...il.com>,
	Simon Jeons <simon.jeons@...il.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <ak@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH v2 1/2] Make the batch size of the percpu_counter
 configurable

On Wed, 22 May 2013 16:37:18 -0700 Tim Chen <tim.c.chen@...ux.intel.com> wrote:

> Currently the per cpu counter's batch size for memory accounting is
> configured as twice the number of cpus in the system.  However,
> for system with very large memory, it is more appropriate to make it
> proportional to the memory size per cpu in the system.
> 
> For example, for a x86_64 system with 64 cpus and 128 GB of memory,
> the batch size is only 2*64 pages (0.5 MB).  So any memory accounting
> changes of more than 0.5MB will overflow the per cpu counter into
> the global counter.  Instead, for the new scheme, the batch size
> is configured to be 0.4% of the memory/cpu = 8MB (128 GB/64 /256),
> which is more inline with the memory size.

I renamed the patch to "mm: tune vm_committed_as percpu_counter
batching size".

Do we have any performance testing results?  They're pretty important
for a performance-improvement patch ;)

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