linux-kernel - Re: [PATCH] mm: remove struct reclaim

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Message-ID: <20111118210941.GK7046@dastard>
Date:	Sat, 19 Nov 2011 08:09:41 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: remove struct reclaim_state

On Fri, Nov 18, 2011 at 02:07:02PM +0400, Konstantin Khlebnikov wrote:
> Dave Chinner wrote:
> >On Fri, Nov 18, 2011 at 01:28:06PM +0300, Konstantin Khlebnikov wrote:
> >>Memory reclaimer want to know how much pages was reclaimed during shrinking slabs.
> >>Currently there is special struct reclaim_state with single counter and pointer from
> >>task-struct. Let's store counter direcly on task struct and account freed pages
> >>unconditionally. This will reduce stack usage and simplify code in reclaimer and slab.
> >>
> >>Logic in do_try_to_free_pages() is slightly changed, but this is ok.
> >>Nobody calls shrink_slab() explicitly before do_try_to_free_pages(),
> >
> >Except for drop_slab() and shake_page()....
> 
> Indeed, but they do not care about accounting reclaimed pages and
> they do not call do_try_to_free_pages() after all.

Right, so you're effectively leaving a landmine for someone to trip
over - anyone that cares about accounting during shrink_slab needs
to zero the value first.  The current code makes this obvious by not
having a reclaim structure in the cases where callers don't care
about accounting - after your change the correct usage is
undocumented....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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