linux-ext4 - Re: [PATCH] ext4: use percpu counter for extent cache count

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Date:	Fri, 01 Mar 2013 12:02:34 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
CC:	Dave Jones <davej@...hat.com>,
	"gnehzuil.liu" <gnehzuil.liu@...il.com>,
	Zheng Liu <wenqing.lz@...bao.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: use percpu counter for extent cache count

On 3/1/13 12:00 PM, Theodore Ts'o wrote:
> On Fri, Mar 01, 2013 at 10:42:25AM -0600, Eric Sandeen wrote:
>> Use a percpu counter rather than atomic types for shrinker accounting.
>> There's no need for ultimate accuracy in the shrinker, so this
>> should come a little more cheaply.  The percpu struct is somewhat
>> large, but there was a big gap before the cache-aligned
>> s_es_lru_lock anyway, and it fits nicely in there.
> 
> I thought about using percpu counters, but I was worried about the
> size on really big machines.  OTOH, it will be the really large NUMA
> machines where atomic_t will really hurt, so maybe we should use
> percpu countesr and not really worry about it.  It's on a per file
> system basis, so even if it is a few hundred bytes it shouldn't break
> the bank.
> 
> 						- Ted
> 

I was mostly keying off what quota felt was best, I guess.
I'm not wedded to either approach, it was just a thought.
So you can take it or leave it. :)

Thanks,
-Eric
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