linux-kernel - Re: [patch 1/3] mm: memcontrol: do not kill uncharge batching in free_pages_and_swap

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Date:	Thu, 2 Oct 2014 11:57:50 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Thelen <gthelen@...gle.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Dave Hansen <dave@...1.net>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/3] mm: memcontrol: do not kill uncharge batching in
 free_pages_and_swap_cache

On Thu, Sep 25, 2014 at 03:44:03PM +0200, Michal Hocko wrote:
> On Wed 24-09-14 17:03:22, Johannes Weiner wrote:
> [...]
> > In release_pages, break the lock at least every SWAP_CLUSTER_MAX (32)
> > pages, then remove the batching from free_pages_and_swap_cache.
> 
> Actually I had something like that originally but then decided to
> not change the break out logic to prevent from strange and subtle
> regressions. I have focused only on the memcg batching POV and led the
> rest untouched.
> 
> I do agree that lru_lock batching can be improved as well. Your change
> looks almost correct but you should count all the pages while the lock
> is held otherwise you might happen to hold the lock for too long just
> because most pages are off the LRU already for some reason. At least
> that is what my original attempt was doing. Something like the following
> on top of the current patch:

Yep, that makes sense.

Would you care to send it in such that Andrew can pick it up?  Thanks!
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