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

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Date:	Tue, 21 May 2013 13:41:22 -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 Fri,  3 May 2013 03:10:52 -0700 Tim Chen <tim.c.chen@...ux.intel.com> wrote:

> Currently, there is a single, global, variable (percpu_counter_batch) that
> controls the batch sizes for every 'struct percpu_counter' on the system.
> 
> However, there are some applications, e.g. memory accounting where it is
> more appropriate to scale the batch size according to the memory size.
> This patch adds the infrastructure to be able to change the batch sizes
> for each individual instance of 'struct percpu_counter'.
> 

This patch seems to add rather a lot of unnecessary code.

- The increase in the size of percu_counter is regrettable.

- The change to percpu_counter_startup() is unneeded - no
  percpu_counters should exist at this time.  (We may have screwed this
  up - percpu_counter_startup() shuold probably be explicitly called
  from start_kernel()).

- Once the percpu_counter_startup() change is removed, all that code
  which got moved out of CONFIG_HOTPLUG_CPU can be put back.

And probably other stuff.


If you want to use a larger batch size for vm_committed_as, why not
just use the existing __percpu_counter_add(..., batch)?  Easy.

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