linux-kernel - Re: ksm: initialize rmap values directly and make them const

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Message-ID: <3192eca4-1c90-44ed-8386-bf635db357c4@kernel.org>
Date: Fri, 6 Feb 2026 19:09:56 +0100
From: "David Hildenbrand (Arm)" <david@...nel.org>
To: Matthew Wilcox <willy@...radead.org>, xu.xin16@....com.cn
Cc: akpm@...ux-foundation.org, chengming.zhou@...ux.dev, hughd@...gle.com,
 wang.yaxin@....com.cn, yang.yang29@....com.cn, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: ksm: initialize rmap values directly and make them const

On 2/6/26 18:34, David Hildenbrand (Arm) wrote:
> On 2/6/26 16:29, Matthew Wilcox wrote:
>> On Fri, Feb 06, 2026 at 03:22:54PM +0800, xu.xin16@....com.cn wrote:
>>> make them const to make code more robust. Besides, since KSM folios 
>>> are always
>>> order-0, so folio_nr_pages(KSM folio) is always 1, so the line:
>>>
>>>     "pgoff_end = pgoff_start + folio_nr_pages(folio) - 1;"
>>>
>>> becomes directly:
>>>
>>>     "pgoff_end = pgoff_start;"
>>
>> How do you know KSM folios will always be order 0?  I don't.  NAK this
>> change.
> 
> Once that changes we can revisit. ACK from me stands.

And just to elaborate a bit: I don't see support for > 0 happening any 
time soon, and it will require significant changes that I am not even 
sure we would want to maintain upstream :)

-- 
Cheers,

David