Re: [PATCH 1/1] shrink dentry cache before inode cache

[Andrew Morton <akpm@osdl.org>]

Cliff Wickman <cpw@sgi.com> wrote:
>
> The shrink_slab() function must often be called twice to get significant
> slab cache reduction.
> 
> shrink_slab() walks the shrinker_list to call functions that can
> release kernel slab memory.
> 
> The shrinker_list is walked head to tail and, as it is now, comes across the
> inode cache shrinker first.  This releases inodes found on the inode_unused 
> list.  Afterwards the dentry cache shrinker moves many freeable inodes to 
> the list.  But those inodes are not freed until a second invocation of 
> shrink_slab().
> 
> The dentry cache shrinker (shrink_dcache_memory()) should run before 
> the inode cache shrinker (shrink_icache_memory()).
> 
> This can be accomplished by queuing the dentry cache shrinker earlier -
> simply calling inode_init() before dcache_init().

Is logical, although the implementation is fragile.  This came up a year or
so ago and we decided it wouldn't make any difference - iirc because slab
shrinking tends to occur in little bites across the whole list.

Do you have any measurements or instrumentation which show improvement?

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