| Message ID | 20230309111258.24079-4-vbabka@suse.cz (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | cleanup vma_merge() and improve mergeability tests | expand |
On Thu, Mar 09, 2023 at 12:12:51PM +0100, Vlastimil Babka wrote: > Case 1 is now shown in the comment as next vma being merged with prev, > so use 'next' instead of 'mid'. In case 1 they both point to the same > vma. > > As a consequence, in case 6, the dup_anon_vma() is now tried first on > 'next' and then on 'mid', before it was the opposite order. This is not > a functional change, as those two vma's cannnot have a different > anon_vma, as that would have prevented the merging in the first place. > This makes me wonder whether there might be further simplifications based upon known conditions of mergeability to be had (as e.g. is_mergeable_anon_vma() would have prevented otherwise). But perhaps I will discover these later in the series :) > Signed-off-by: Vlastimil Babka <vbabka@suse.cz> > --- > mm/mmap.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 1af4c9bc2c87..c33237b283c9 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -605,7 +605,7 @@ static inline void vma_complete(struct vma_prepare *vp, > > /* > * In mprotect's case 6 (see comments on vma_merge), > - * we must remove the one after next as well. > + * we are removing both mid and next vmas > */ > if (vp->remove2) { > vp->remove = vp->remove2; > @@ -948,13 +948,14 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, > /* Can we merge both the predecessor and the successor? */ > if (merge_prev && merge_next && > is_mergeable_anon_vma(prev->anon_vma, next->anon_vma, NULL)) { > - remove = mid; /* case 1 */ > + remove = next; /* case 1 */ > vma_end = next->vm_end; > - err = dup_anon_vma(prev, mid); > + err = dup_anon_vma(prev, next); > if (mid != next) { /* case 6 */ > + remove = mid; > remove2 = next; > - if (!mid->anon_vma) > - err = dup_anon_vma(prev, next); > + if (!next->anon_vma) > + err = dup_anon_vma(prev, mid); > } > } else if (merge_prev) { > err = 0; /* case 2 */ > -- > 2.39.2 > Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
diff --git a/mm/mmap.c b/mm/mmap.c index 1af4c9bc2c87..c33237b283c9 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -605,7 +605,7 @@ static inline void vma_complete(struct vma_prepare *vp, /* * In mprotect's case 6 (see comments on vma_merge), - * we must remove the one after next as well. + * we are removing both mid and next vmas */ if (vp->remove2) { vp->remove = vp->remove2; @@ -948,13 +948,14 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, /* Can we merge both the predecessor and the successor? */ if (merge_prev && merge_next && is_mergeable_anon_vma(prev->anon_vma, next->anon_vma, NULL)) { - remove = mid; /* case 1 */ + remove = next; /* case 1 */ vma_end = next->vm_end; - err = dup_anon_vma(prev, mid); + err = dup_anon_vma(prev, next); if (mid != next) { /* case 6 */ + remove = mid; remove2 = next; - if (!mid->anon_vma) - err = dup_anon_vma(prev, next); + if (!next->anon_vma) + err = dup_anon_vma(prev, mid); } } else if (merge_prev) { err = 0; /* case 2 */
Case 1 is now shown in the comment as next vma being merged with prev, so use 'next' instead of 'mid'. In case 1 they both point to the same vma. As a consequence, in case 6, the dup_anon_vma() is now tried first on 'next' and then on 'mid', before it was the opposite order. This is not a functional change, as those two vma's cannnot have a different anon_vma, as that would have prevented the merging in the first place. Signed-off-by: Vlastimil Babka <vbabka@suse.cz> --- mm/mmap.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)