Re: [RFC, PATCH] Make memory reclaim from inodes and dentry cachemore scalable

From: Tim Chen
Date: Tue May 08 2012 - 16:00:34 EST

On Wed, 2012-05-02 at 15:06 -0700, Tim Chen wrote:
> The following patch detects when inodes and dentries cache are really
> low in free entries, and skip reclamation of memory from them when it is
> futile to do so. We only resume reclaiming memory from inodes and
> dentries cache when we have a reasonable amount of memory there.
> This avoided us bottlenecking on sb_lock to do useless memory
> reclamation.
> I assume that it is okay to check super block's number of free objects
> content without sb_lock as we are holding shrinker list's read lock. The
> shrinker is still registered so super block is not yet deactivated which
> requires shrinker un-registration. It will be great if Al can help to
> comment on whether this assumption is okay.
> In a test scenario where page cache is putting heavy pressure on memory
> usage with large number of processes, we saw very heavy contention on
> the sb_lock to get free pages as seen in the following profile. The
> patch helped to reduce the runtime by almost a factor of 4.
> 62.81% cp [kernel.kallsyms] [k] _raw_spin_lock
> |
> --- _raw_spin_lock
> |
> |--45.19%-- grab_super_passive
> | prune_super
> | shrink_slab
> | do_try_to_free_pages
> | try_to_free_pages
> | __alloc_pages_nodemask
> | alloc_pages_current
> Tim

Hi Al,

Want to ping you again to see what your thoughts are on this patch I've
sent a week ago.



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