Re: [PATCH 13/30] mm/vma: refactor vmg_adjust_set_range() for clarity

[Lorenzo Stoakes]

On Thu, Jul 09, 2026 at 11:18:40AM -0400, Gregory Price wrote:
> On Mon, Jun 29, 2026 at 01:23:24PM +0100, Lorenzo Stoakes wrote:
> > Add comments with ASCII diagrams to describe what we're doing, avoid
> > dubious use of PHYS_PFN(), and use vma_start_pgoff().
> >
> > The most complicated scenario represented here is vmg->__adjust_next_start
> > - when this is set, vmg->[start, end] actually indicate the range to be
> > retained, so take special care to describe this accurately.
> >
> > No functional change intended.
> >
> > Signed-off-by: Lorenzo Stoakes <ljs@xxxxxxxxxx>
>
> Reviewed-by: Gregory Price <gourry@xxxxxxxxxx>
>
> > +		/*
> > +		 * vmg->start    vmg->end
> > +		 * |             |
> > +		 * v    merge    v
> > +		 * <------------->
> > +		 *         delta
> > +		 *        <------>
> > +		 * |------|----------------|
> > +		 * | prev |    middle      |
> > +		 * |------|----------------|
> > +		 *        ^
> > +		 *        |
> > +		 *        middle->vm_start
> > +		 */
>
> Even with these diagrams, it's a bit difficult to understand what the
> actual intent/result of this chunk is (but that may be a limitation of
> me not spending enough time reading the surrounding code, not a comment
> of your work here).

Yeah I know, I do hope to refactor all this at some point to make it simpler,
but for the time being tried to make the confusing thing at least _slightly_
less confusing :)

>
> ~Gregory

Cheers, Lorenzo

>
> > +		/*
> > +		 *                Originally:
> > +		 *
> > +		 *            vmg->start   vmg->end
> > +		 *            |            |
> > +		 *            v    merge   v
> > +		 *            <------------>
> > +		 *            .            .
> > +		 * merge_existing_range() updates to:
> > +		 *            .            .
> > +		 * vmg->start vmg->end     .
> > +		 * |          |            .
> > +		 * v  retain  v            .
> > +		 * <---------->            .
> > +		 *             delta       .
> > +		 *            <----->      .
> > +		 * |----------------|------|
> > +		 * |    middle      | next |
> > +		 * |----------------|------|
> > +		 *                  ^
> > +		 *                  |
> > +		 *                  next->vm_start
> > +		 */