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

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:

quoted

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@kernel.org>

Reviewed-by: Gregory Price <gourry@gourry.net>

quoted

+		/*
+		 * 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

quoted

+		/*
+		 *                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
+		 */