linux-kernel - Re: [PATCH v2 2/2] vmscan: shrink_slab() require number of lru

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Message-Id: <20100709092124.CD5A.A69D9226@jp.fujitsu.com>
Date:	Fri,  9 Jul 2010 09:46:32 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, Mel Gorman <mel@....ul.ie>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH v2 2/2] vmscan: shrink_slab() require number of lru_pages, not page order

> On Thu, 8 Jul 2010, Andrew Morton wrote:
> 
> > > AFAICT this is not argument error but someone changed the naming of the
> > > parameter.
> >
> > It's been there since day zero:
> >
> > : commit 2a16e3f4b0c408b9e50297d2ec27e295d490267a
> > : Author:     Christoph Lameter <clameter@...r.sgi.com>
> > : AuthorDate: Wed Feb 1 03:05:35 2006 -0800
> > : Commit:     Linus Torvalds <torvalds@...osdl.org>
> > : CommitDate: Wed Feb 1 08:53:16 2006 -0800
> > :
> > :     [PATCH] Reclaim slab during zone reclaim
> 
> That only shows that the order parameter was passed to shrink_slab() which
> is what I remember being done intentionally.
> 
> Vaguely recall that this was necessary to avoid shrink_slab() throwing out
> too many pages for higher order allocs.

But It make opposite effect. number of scanning objects of shrink_slab() are

                          lru_scanned        max_pass
basic_scan_objects = 4 x -------------  x -----------------------------
                          lru_pages        shrinker->seeks (default:2)

scan_objects = min(basic_scan_objects, max_pass * 2)


That said, small lru_pages parameter makes too many slab dropping.
Practically, zone-reclaim always take max_pass*2. about inode, 
shrink_icache_memory() takes number of unused inode as max_pass.
It mean one shrink_slab() calling drop all icache. Is this optimal
behavior? why?

Am I missing something?

> Initially zone_reclaim was full of heuristics that later were replaced by
> counter as the new ZVCs became available and gradually better ways of
> accounting for pages became possible.


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