linux-kernel - Re: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86

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Date:   Thu, 30 Mar 2017 08:45:56 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     "Huang\, Ying" <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <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 -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64

Johannes Weiner <hannes@...xchg.org> writes:

> On Tue, Mar 28, 2017 at 01:32:01PM +0800, Huang, Ying wrote:
>> @@ -499,6 +499,19 @@ config FRONTSWAP
>>  
>>  	  If unsure, say Y to enable frontswap.
>>  
>> +config ARCH_USES_THP_SWAP_CLUSTER
>> +	bool
>> +	default n
>
> This is fine.
>
>> +config THP_SWAP_CLUSTER
>> +	bool
>> +	depends on SWAP && TRANSPARENT_HUGEPAGE && ARCH_USES_THP_SWAP_CLUSTER
>> +	default y
>> +	help
>> +	  Use one swap cluster to hold the contents of the THP
>> +	  (Transparent Huge Page) swapped out.  The size of the swap
>> +	  cluster will be same as that of THP.
>
> But this is a super weird thing to ask the user. How would they know
> what to say, if we don't know? I don't think this should be a config
> knob at all. Merge the two config items into a simple

The user will not see this, because there is no string after "bool" to
let user to select it.  The help here is for document only, so that
architecture developers could know what this is for.

> config THP_SWAP_CLUSTER
>      bool
>      default n
>
> and let the archs with reasonable THP sizes select it.

This will have same effect as the original solution except the document
is removed.

Best Regards,
Huang, Ying