Subject: Re: [PATCH -mmotm 1/5] memcg: disable irq at page cgroup lock
From: Peter Zijlstra <peterz@infradead.org>
To: Greg Thelen <gthelen@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>,
       Vivek Goyal <vgoyal@redhat.com>, balbir@linux.vnet.ibm.com,
       Andrea Righi <arighi@develer.com>,
       Trond Myklebust <trond.myklebust@fys.uio.no>,
       Suleiman Souhlal <suleiman@google.com>,
       "Kirill A. Shutemov" <kirill@shutemov.name>,
       Andrew Morton <akpm@linux-foundation.org>,
       containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org
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Date: Fri, 23 Apr 2010 23:19:09 +0200
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On Fri, 2010-04-23 at 13:17 -0700, Greg Thelen wrote:
> 
> This is an interesting idea.  If this applies to memcg dirty accounting,
> then would it also apply to system-wide dirty accounting?  I don't think
> so, but I wanted to float the idea.  It looks like this proportions.c
> code is good is at comparing the rates of events (for example: per-task
> dirty page events).  However, in the case of system-wide dirty
> accounting we also want to consider the amount of dirty memory, not just
> the rate at which it is being dirtied.

Correct, the whole proportion thing is purely about comparing rates of
events.

> The performance of simple irqsave locking or more advanced RCU locking
> is similar to current locking (non-irqsave/non-rcu) for several
> workloads (kernel build, dd).  Using a micro-benchmark some differences
> are seen:
> * irqsave is 1% slower than mmotm non-irqsave/non-rcu locking.
> * RCU locking is 4% faster than mmotm non-irqsave/non-rcu locking.
> * RCU locking is 5% faster than irqsave locking.

Depending on what architecture you care about local_t might also be an
option, it uses per-cpu irq/nmi safe instructions (and falls back to
local_irq_save/restore for architectures lacking this support).


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