Why isn't shrink_slab more zone oriented ?

Why isn't shrink_slab more zone oriented ?

[kautuk.c @samsung.com]

Hi,

I was going through the do_try_to_free_pages(), balance_pgdat(),
__zone_reclaim()
functions and I see that shrink_zone and shrink_slab are called for each zone.

But, shrink_slab() doesn't seem to bother about the zone from where it
is freeing
memory.

My questions are:

- Will this be a strain on the direct/indirect reclamation algorithm ?
  The loops involved expects to free something from that particular zone.
  shrink_slab might take more time than is required to free up pages from that
  particular zone which might not be optimal.
  Am I right about this conclusion ?

- If the above is correct, then is there any work happening on this
front, i.e., to
  make shrink_slab functionality and the shrinker callbacks more zone-centric ?
  Are there any patches that I could look at or download from
somewhere for this ?

- Are there any other considerations to be careful of for making
shrink_slab more
  zone centric ? Can there be other side effects that affects
performance if the
  shrink_slab and shrinker callbacks are made to free pages only from
a particular
  zone ?

Thanks,
Kautuk.

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Re: Why isn't shrink_slab more zone oriented ?

[Dave Chinner]

On Mon, Sep 26, 2011 at 05:21:12PM +0530, kautuk.c @samsung.com wrote:
> Hi,
> 
> I was going through the do_try_to_free_pages(), balance_pgdat(),
> __zone_reclaim()
> functions and I see that shrink_zone and shrink_slab are called for each zone.
> 
> But, shrink_slab() doesn't seem to bother about the zone from where it
> is freeing
> memory.

Work is in progress to do this.

http://lwn.net/Articles/456071/

Dirty slab objects are currently not tracked in a manner that makes
per-zone reclaim efficient to do, os that needs to be corrected
first.  Once we have generic per-zone LRU infrastructure, then we
can easily push zone reclaim hints down into the shrinkers for them
to scan the appropriate LRU....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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