On 3/22/23 10:06, Vlastimil Babka wrote:
> On 3/22/23 08:13, Lorenzo Stoakes wrote:
>> Use find_vma_intersection() and vma_lookup() to both simplify the logic and
>> to fold the end == next->vm_start condition into one block.
>>
>> 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.
>
> I'm not so sure...
Disregard that, vma_lookup() is not find_vma(). Next cleanup challenge: more
obvious naming of those two.
>> Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
>> ---
>> mm/mmap.c | 24 +++++++++++-------------
>> 1 file changed, 11 insertions(+), 13 deletions(-)
>>
>> diff --git a/mm/mmap.c b/mm/mmap.c
>> index c9834364ac98..dbdbb92493b2 100644
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -930,15 +930,14 @@ 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 || /* cases 1 - 4 */
>> + end == curr->vm_end) /* cases 6 - 8, adjacent VMA */
>> + next = vma_lookup(mm, end);
>
> AFAICS if the next vma is not adjacent to CCCC or ****, but there's a gap,
> this will still give you a non-NULL result?
>
>> + else
>> + next = NULL; /* case 5 */
>>
>> /* verify some invariant that must be enforced by the caller */
>> VM_WARN_ON(prev && addr <= prev->vm_start);
>> @@ -959,11 +958,10 @@ 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 &&
>
> And then without this end == next->vm_start check, merge will be done
> despite the gap.
>
>> - 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
>
