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Date: Mon, 14 May 2012 16:51:21 +0800
From: Cong Wang <xiyou.wangcong@gmail.com>
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To: Sasha Levin <levinsasha928@gmail.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
        Minchan Kim <minchan@kernel.org>, Hugh Dickins <hughd@google.com>,
        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
References: <alpine.LSU.2.00.1205110054520.2801@eggly.anvils> <CA+1xoqcChazS=TRt6-7GjJAzQNFLFXmO623rWwjRkdD5x3k=iw@mail.gmail.com> <4FACD00D.4060003@kernel.org> <4FACD573.4060103@kernel.org> <CA+55aFxsZqU4bXRz61ngnR2ozH=AAhwGHR+PqzdTRfnCxJY0oQ@mail.gmail.com> <CA+1xoqc15HY1rECsJ6Aj1WMzwT12z4DByJhFopyBAiKawEFh3Q@mail.gmail.com>
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On 05/12/2012 12:35 AM, Sasha Levin wrote:
> On Fri, May 11, 2012 at 6:27 PM, Linus Torvalds
> <torvalds@linux-foundation.org>  wrote:
>> On Fri, May 11, 2012 at 2:01 AM, Minchan Kim<minchan@kernel.org>  wrote:
>>>
>>> I didn't have a time so made quick patch to show just concept.
>>> Not tested and Not consider carefully.
>>> If anyone doesn't oppose, I will send formal patch which will have more beauty code.
>>
>> What's so magical about that '8' *anyway*? We do we have that minimum at all?
>>
>> At the very least, the 8-vs-0 thing needs to be explained.
>
> The '0' acts as an "off" switch.
>
> Once it's on, we reserve 1/x of the pages for the pagelists. I'm not
> sure why 8 was selected in the first place, but I guess it made sense
> that you don't want to reserve 15%+ of your memory for the pagelists.

1/x is not user-friendly, other vm sysctl's use percentage (x%), for 
example, overcommit_ratio.