linux-kernel - Re: [PATCH] mm: raise MemFree by reverting percpu_pagelist

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Message-ID: <alpine.LSU.2.00.1205110656540.5839@eggly.anvils>
Date:	Fri, 11 May 2012 07:10:01 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Minchan Kim <minchan@...nel.org>
cc:	Sasha Levin <levinsasha928@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: raise MemFree by reverting percpu_pagelist_fraction
 to 0

On Fri, 11 May 2012, Minchan Kim wrote:
> On 05/11/2012 05:30 PM, Sasha Levin wrote:
> 
> >> Commit 93278814d359 "mm: fix division by 0 in percpu_pagelist_fraction()"
> >> mistakenly initialized percpu_pagelist_fraction to the sysctl's minimum 8,
> >> which leaves 1/8th of memory on percpu lists (on each cpu??); but most of
> >> us expect it to be left unset at 0 (and it's not then used as a divisor).
> > 
> > I'm a bit confused about this, does it mean that once you set
> > percpu_pagelist_fraction to a value above the minimum, you can no
> > longer set it back to being 0?
> 
> 
> Unfortunately, Yes. :(
> It's rather awkward and need fix.

It's inelegant, but does that actually need a fix?  Has anybody asked
for that option in the six years of percpu_pagelist_fraction?

Does setting percpu_pagelist_fraction to some large number perhaps
approximate to the default behaviour of percpu_pagelist_fraction 0?

I don't care very much either way - just don't want this discussion
to divert from applying last night's fix to the default behaviour
that most people expect.

Hugh
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