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

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Message-ID: <39fb9e1b-b806-47da-a711-20c6cc12913a@lucifer.local>
Date: Mon, 11 Aug 2025 10:25:56 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Alejandro Colomar <alx@...nel.org>
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 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'?

>
> > 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/>