* Lorenzo Stoakes <lstoakes@xxxxxxxxx> [230321 16:51]:
> We are only interested in next if end == next->vm_start (in which case we
> check to see if we can set merge_next), so perform this check alongside
> checking whether curr should be set.
>
> This groups all of the simple range checks together and establishes the
> invariant that, if prev, curr or next are non-NULL then their positions are
> as expected.
>
> This has no functional impact.
>
> Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
> ---
> mm/mmap.c | 25 ++++++++++++-------------
> 1 file changed, 12 insertions(+), 13 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index c9834364ac98..6361baf75601 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -930,15 +930,15 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
> if (vm_flags & VM_SPECIAL)
> return NULL;
>
> - curr = find_vma(mm, prev ? prev->vm_end : 0);
> - if (curr && curr->vm_end == end) /* cases 6, 7, 8 */
> - next = find_vma(mm, curr->vm_end);
> - else
> - next = curr;
> + /* Does the input range span an existing VMA? (cases 5 - 8) */
> + curr = find_vma_intersection(mm, prev ? prev->vm_end : 0, end);
>
> - /* In cases 1 - 4 there's no CCCC vma */
> - if (curr && end <= curr->vm_start)
> - curr = NULL;
> + if (curr && end == curr->vm_end)
> + /* Is there is a VMA immediately adjacent (cases 6 - 8)? */
> + next = vma_lookup(mm, curr->vm_end);
Since end == curr->vm_end, this lookup is the same as below so these two
statements can be combined.
I also think you may need to initialize next to null since it may not be
set for the 'cannot merge' case.
Something like:
if ((!curr) || /* case 1-4 */
(end == curr->vm_end)) /* Case 6-8, adjacent vma */
next = vma_lookup(mm, end);
else
next = NULL
> + else if (!curr)
> + /* Is there a VMA next to a hole (case 1 - 3) or prev (4)? */
> + next = vma_lookup(mm, end);
Nit, can we have braces for comments that make the if/else look like
it's unguarded?
>
> /* verify some invariant that must be enforced by the caller */
> VM_WARN_ON(prev && addr <= prev->vm_start);
> @@ -959,11 +959,10 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
> }
> }
> /* Can we merge the successor? */
> - if (next && end == next->vm_start &&
> - mpol_equal(policy, vma_policy(next)) &&
> - can_vma_merge_before(next, vm_flags,
> - anon_vma, file, pgoff+pglen,
> - vm_userfaultfd_ctx, anon_name)) {
> + if (next && mpol_equal(policy, vma_policy(next)) &&
> + can_vma_merge_before(next, vm_flags,
> + anon_vma, file, pgoff+pglen,
> + vm_userfaultfd_ctx, anon_name)) {
> merge_next = true;
> }
>
> --
> 2.39.2
>
