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

[Tim Chen <tim.c.chen@linux.intel.com>]

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.

Thanks.

Tim