From: Minchan Kim <minchan@kernel.org>
To: Hugh Dickins <hughd@google.com>
Cc: Sasha Levin <levinsasha928@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: raise MemFree by reverting percpu_pagelist_fraction to 0
Date: Mon, 14 May 2012 10:51:51 +0900 [thread overview]
Message-ID: <4FB06537.4070205@kernel.org> (raw)
In-Reply-To: <alpine.LSU.2.00.1205110656540.5839@eggly.anvils>
Hi Hugh,
On 05/11/2012 11:10 PM, Hugh Dickins wrote:
> 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?
I don't have heard about it but thing we can't reset to 0 again once we set some number to above 8 is
very strange. Sometime, someone may raise the value on /proc/sys/vm/percpu_pagelist_fraction to test it
and realized function of the knob so he want to reset it to 0 default value, again. But he couldn't.
It's very strange. :(
>
> Does setting percpu_pagelist_fraction to some large number perhaps
> approximate to the default behaviour of percpu_pagelist_fraction 0?
Yes. But it's not intuitive.
>
> 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.
Of course.
It's totally from my careless review.
Actually, I didn't find to change default value to 8 when I review the patch.
I just focused on proc_dointvec_minmax's err return value.
Shame on me. :(
Thanks for spot it.
>
> Hugh
>
> --
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--
Kind regards,
Minchan Kim
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next prev parent reply other threads:[~2012-05-14 1:51 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-11 8:00 [PATCH] mm: raise MemFree by reverting percpu_pagelist_fraction to 0 Hugh Dickins
2012-05-11 8:30 ` Sasha Levin
2012-05-11 8:38 ` Minchan Kim
2012-05-11 9:01 ` Minchan Kim
2012-05-11 16:27 ` Linus Torvalds
2012-05-11 16:35 ` Sasha Levin
2012-05-11 16:54 ` Linus Torvalds
2012-05-14 8:51 ` Cong Wang
2012-05-11 14:10 ` Hugh Dickins
2012-05-14 1:51 ` Minchan Kim [this message]
2012-05-11 16:26 ` Linus Torvalds
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