linux-kernel - Re: [PATCH -v3 01/10] mm, swap: Make swap cluster size same of THP size on x86

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Message-ID: <87a8fi5kpz.fsf@yhuang-mobile.sh.intel.com>
Date:   Thu, 08 Sep 2016 11:07:20 -0700
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     "Huang\, Ying" <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <tim.c.chen@...el.com>, <dave.hansen@...el.com>,
        <andi.kleen@...el.com>, <aaron.lu@...el.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, Hugh Dickins <hughd@...gle.com>,
        Shaohua Li <shli@...nel.org>, Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH -v3 01/10] mm, swap: Make swap cluster size same of THP size on x86_64

Anshuman Khandual <khandual@...ux.vnet.ibm.com> writes:

> On 09/07/2016 10:16 PM, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@...el.com>
>> 
>> In this patch, the size of the swap cluster is changed to that of the
>> THP (Transparent Huge Page) on x86_64 architecture (512).  This is for
>> the THP swap support on x86_64.  Where one swap cluster will be used to
>> hold the contents of each THP swapped out.  And some information of the
>> swapped out THP (such as compound map count) will be recorded in the
>> swap_cluster_info data structure.
>> 
>> For other architectures which want THP swap support, THP_SWAP_CLUSTER
>> need to be selected in the Kconfig file for the architecture.
>> 
>> In effect, this will enlarge swap cluster size by 2 times on x86_64.
>> Which may make it harder to find a free cluster when the swap space
>> becomes fragmented.  So that, this may reduce the continuous swap space
>> allocation and sequential write in theory.  The performance test in 0day
>> shows no regressions caused by this.
>
> This patch needs to be split into two separate ones
>
> (1) Add THP_SWAP_CLUSTER config option
> (2) Enable CONFIG_THP_SWAP_CLUSTER for X86_64
>
> The first patch should explain the proposal and the second patch
> should have 86_64 arch specific details, regressions etc as already
> been explained in the commit message.

The code change and possible issues is not x86_64 specific, but general
for all architectures where the config option is enabled.  If so, the
second patch becomes 1 line kconfig change and no much to be said in
patch description.  Does it deserve a separate patch?

Best Regards,
Huang, Ying