Commit 642c66d8 authored by Wei Yang's avatar Wei Yang Committed by Andrew Morton
Browse files

mm/vma: the pgoff is correct if can_merge_right 

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.


[akpm@linux-foundation.org: remove now-unused local]
[lorenzo.stoakes@oracle.com: rephrase the changelog]
Link: https://lkml.kernel.org/r/20241024093347.18057-1-richard.weiyang@gmail.com


Signed-off-by: default avatarWei Yang <richard.weiyang@gmail.com>
Reviewed-by: default avatarLorenzo 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 5ac87a88

mm/vma.c

+0 −3
Original line number Diff line number Diff line
@@ -962,9 +962,7 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg) 
{

	struct vm_area_struct *prev = vmg->prev;

	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 +984,6 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg) 
	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. */