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

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Message-ID: <aYY3tZmsIQnT0b3V@casper.infradead.org>
Date: Fri, 6 Feb 2026 18:49:25 +0000
From: Matthew Wilcox <willy@...radead.org>
To: "David Hildenbrand (Arm)" <david@...nel.org>
Cc: xu.xin16@....com.cn, 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 Fri, Feb 06, 2026 at 07:09:56PM +0100, David Hildenbrand (Arm) wrote:
> 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 :)

OK, you're the KSM maintainer.  There doesn't seem to be anywhere else
in the KSM code which handles large folios, so this is just removing
code that was recently added?