linux-kernel - Re: [PATCH v4 1/2] man/man2/mremap.2: describe multiple mapping move

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Message-ID: <s2lpafv4ldpmwkx2455t3l566fnkrlid7upwfuebod3lyy25hm@lvokcxytqow7>
Date: Mon, 11 Aug 2025 11:37:35 +0200
From: Alejandro Colomar <alx@...nel.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: linux-man@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, 
	Peter Xu <peterx@...hat.com>, Alexander Viro <viro@...iv.linux.org.uk>, 
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	"Liam R . Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>, 
	Pedro Falcato <pfalcato@...e.de>, Rik van Riel <riel@...riel.com>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH v4 1/2] man/man2/mremap.2: describe multiple mapping move

On Mon, Aug 11, 2025 at 10:25:56AM +0100, Lorenzo Stoakes wrote:
> On Mon, Aug 11, 2025 at 11:20:05AM +0200, Alejandro Colomar wrote:
> > Hi Lorenzo,
> >
> > On Mon, Aug 11, 2025 at 06:30:38AM +0100, Lorenzo Stoakes wrote:
> > > > > +Mappings can also simply be moved
> > > > > +(without any resizing)
> > > > > +by specifying equal
> > > > > +.I old_size
> > > > > +and
> > > > > +.I new_size
> > > > > +and using the
> > > > > +.B MREMAP_FIXED
> > > > > +flag
> > > > > +(see below).
> > > > > +Since Linux 6.17,
> > > > > +while
> > > > > +.I old_address
> > > > > +must reside within a mapping,
> > > >
> > > > I don't understand this.  What does it mean that old_address must reside
> > > > within a mapping?  It's a point, not a size, so I'm not sure I
> > > > understand it.
> > >
> > > I think if it were a size it would be more confusing no?
> > >
> > > It's an address, the address must be located within an existing memory mapping.
> >
> > What I don't understand is: how could you not comply with that?  Could
> > you pass some old_address that is in two mappings?  Being a single
> > address, that would be impossible, right?
> 
> It can be in an unmapped area. It's either in an unmapped area or a mapped one.
> 
> I could simply reword this as 'old_address must be mapped'?

Yup, that seems better.  Thanks!

Cheers,
Alex

> > > Will replace with 'located' for clarity.
> > >
> > > >
> > > > > +.I old_size
> > > > > +may span multiple mappings
> > > > > +which do not have to be
> > > > > +adjacent to one another when
> > > > > +performing a move like this.
> >
> >
> > Have a lovely day!
> > Alex
> >
> > --
> > <https://www.alejandro-colomar.es/>

-- 
<https://www.alejandro-colomar.es/>

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