* Lorenzo Stoakes <lstoakes@xxxxxxxxx> [230318 07:15]:
> 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.
>
> Additionally, use the abstract 'vma' object to look up the possible curr or
> next VMA in order to avoid any confusion as to what these variables
> represent - now curr and next are assigned once and only once.
>
> This has no functional impact.
>
> Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
> ---
> mm/mmap.c | 61 ++++++++++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 49 insertions(+), 12 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index c9834364ac98..66893fc72e03 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -930,15 +930,53 @@ 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;
> + /*
> + * If there is a previous VMA specified, find the next, otherwise find
> + * the first.
> + */
> + vma = find_vma(mm, prev ? prev->vm_end : 0);
> +
> + /*
> + * Does the input range span an existing VMA? If so, we designate this
> + * VMA 'curr'. The caller will have ensured that curr->vm_start == addr.
> + *
> + * Cases 5 - 8.
> + */
> + if (vma && end > vma->vm_start) {
> + curr = vma;
It might be better to set:
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)
> + /*
> + * If the addr - end range spans this VMA entirely, then we
> + * check to see if another VMA follows it.
> + *
> + * If it is _immediately_ adjacent (checked below), then we
> + * designate it 'next' (cases 6 - 8).
> + */
> + if (curr->vm_end == end)
> + vma = find_vma(mm, curr->vm_end);
You can change this to:
next = vma_lookup(mm, curr->vm_end);
Then you don't need to validate below, in this case.
> + else
> + /* Case 5. */
> + vma = NULL;
> + } else {
> + /*
> + * The addr - end range either spans the end of prev or spans no
> + * VMA at all - in either case we dispense with 'curr' and
> + * maintain only 'prev' and (possibly) 'next'.
Possibly next here would be:
next = vma_lookup(mm, end);
I think?
> + *
> + * Cases 1 - 4.
> + */
> curr = NULL;
> + }
> +
> + /*
> + * We only actually examine the next VMA if it is immediately adjacent
> + * to end which sits either at the end of a hole (cases 1 - 3), PPPP
> + * (case 4) or CCCC (cases 6 - 8).
> + */
> + if (vma && end == vma->vm_start)
> + next = vma;
> + else
> + next = NULL;
If I'm correct above, then we can drop this next checking.
>
> /* verify some invariant that must be enforced by the caller */
> VM_WARN_ON(prev && addr <= prev->vm_start);
> @@ -959,11 +997,10 @@ 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)) {
I think we can keep this chunk with the next = vma_lookup() changes as
well.
> merge_next = true;
> }
>
> --
> 2.39.2
>
