+ mm-vma-the-pgoff-is-correct-if-can_merge_right.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/vma: the pgoff is correct if can_merge_right
has been added to the -mm mm-unstable branch.  Its filename is
     mm-vma-the-pgoff-is-correct-if-can_merge_right.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vma-the-pgoff-is-correct-if-can_merge_right.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Wei Yang <richard.weiyang@gmail.com>
Subject: mm/vma: the pgoff is correct if can_merge_right
Date: Thu, 24 Oct 2024 09:33:47 +0000

By this point can_vma_merge_right() must have returned true, which implies
can_vma_merge_before() also returned true, which already asserts that the
pgoff is as expected for a merge with the following VMA, thus this
assignment is redundant.

Below is a more detail explanation.

Current definition of can_vma_merge_right() is:

	static bool can_vma_merge_right(struct vma_merge_struct *vmg,
					bool can_merge_left)
	{
		if (!vmg->next || vmg->end != vmg->next->vm_start ||
		    !can_vma_merge_before(vmg))
			return false;
		...
	}

And:

	static bool can_vma_merge_before(struct vma_merge_struct *vmg)
	{
		pgoff_t pglen = PHYS_PFN(vmg->end - vmg->start);
	...
			if (vmg->next->vm_pgoff == vmg->pgoff + pglen)
				return true;
	...
	}

Which implies vmg->pgoff == vmg->next->vm_pgoff - pglen.

None of these values are changed between the check and prior assignment,
so this was an entirely redundant assignment.

[lorenzo: rephrase the change log]

Link: https://lkml.kernel.org/r/20241024093347.18057-1-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/vma.c |    2 --
 1 file changed, 2 deletions(-)

--- a/mm/vma.c~mm-vma-the-pgoff-is-correct-if-can_merge_right
+++ a/mm/vma.c
@@ -964,7 +964,6 @@ struct vm_area_struct *vma_merge_new_ran
 	struct vm_area_struct *next = vmg->next;
 	unsigned long start = vmg->start;
 	unsigned long end = vmg->end;
-	pgoff_t pglen = PHYS_PFN(end - start);
 	bool can_merge_left, can_merge_right;
 	bool just_expand = vmg->merge_flags & VMG_FLAG_JUST_EXPAND;
 
@@ -986,7 +985,6 @@ struct vm_area_struct *vma_merge_new_ran
 	if (can_merge_right) {
 		vmg->end = next->vm_end;
 		vmg->vma = next;
-		vmg->pgoff = next->vm_pgoff - pglen;
 	}
 
 	/* If we can merge with the previous VMA, adjust vmg accordingly. */
_

Patches currently in -mm which might be from richard.weiyang@gmail.com are

maple_tree-i-is-always-less-than-or-equal-to-mas_end.patch
maple_tree-goto-complete-directly-on-a-pivot-of-0.patch
maple_tree-remove-maple_big_nodeparent.patch
maple_tree-memset-maple_big_node-as-a-whole.patch
maple_tree-root-node-could-be-handled-by-p_slot-too.patch
maple_tree-clear-request_count-for-new-allocated-one.patch
maple_tree-total-is-not-changed-for-nomem_one-case.patch
maple_tree-simplify-mas_push_node.patch
maple_tree-calculate-new_end-when-needed.patch
maple_tree-remove-sanity-check-from-mas_wr_slot_store.patch
mm-vma-the-pgoff-is-correct-if-can_merge_right.patch