linux-ext4 - Re: [PATCH] ext4: optimize ext4_es

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Date:	Fri, 01 Mar 2013 10:40:37 -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: optimize ext4_es_shrink()

On 2/28/13 11:00 PM, Theodore Ts'o wrote:
> When the system is under memory pressure, ext4_es_srhink() will get
> called very often.  So optimize returning the number of items in the
> file system's extent status cache by keeping a per-filesystem count,
> instead of calculating it each time by scanning all of the inodes in
> the extent status cache.
> 
> Also rename the slab used for the extent status cache to be
> "ext4_extent_status" so it's obviousl the slab in question is created
> by ext4.

Certainly better than walking an arbitrarily long list.  :)
So:

Reviewed-by: Eric Sandeen <sandeen@...hat.com>

I was wondering a couple things, though - 

1) should this one be scaled by the vfs_cache_pressure sysctl?

2) Also, given that this is only for shrinker accounting, do we need the
precision of the atomic counter? I see that quota uses a per-cpu counter.
Would a percpu counter be any more efficient?  I'll follow
w/ a patch.

-Eric
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