Messages in this thread | | | Date | Mon, 20 Mar 2023 12:27:08 -0400 | From | "Liam R. Howlett" <> | Subject | Re: [PATCH 2/4] mm/mmap/vma_merge: set next to NULL if not applicable |
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* Lorenzo Stoakes <lstoakes@gmail.com> [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@gmail.com> > --- > 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 >
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