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| author | Lorenzo Stoakes <lorenzo.stoakes@oracle.com> | 2025-01-31 12:31:51 +0000 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2025-03-16 22:06:02 -0700 |
| commit | fe3e9cf0d7a28d333523189d1405770d980b07d6 (patch) | |
| tree | 303b26812e1a5f1a66b2fd8f3ac7b262443e0299 /mm/vma.c | |
| parent | 6ab2d9c7c680c0a041477126722cebe7dc57f713 (diff) | |
| download | tip-fe3e9cf0d7a28d333523189d1405770d980b07d6.tar.gz | |
mm: eliminate adj_start parameter from commit_merge()
Introduce internal vmg->__adjust_middle_start and vmg->__adjust_next_start
merge flags, enabling us to indicate to commit_merge() that we are
performing a merge which either spans only part of vmg->middle, or part of
vmg->next respectively.
In the former instance, we change the start of vmg->middle to match the
attributes of vmg->prev, without spanning all of vmg->middle.
This implies that vmg->prev->vm_end and vmg->middle->vm_start are both
increased to form the new merged VMA (vmg->prev) and the new subsequent
VMA (vmg->middle).
In the latter case, we change the end of vmg->middle to match the
attributes of vmg->next, without spanning all of vmg->next.
This implies that vmg->middle->vm_end and vmg->next->vm_start are both
decreased to form the new merged VMA (vmg->next) and the new prior VMA
(vmg->middle).
Since we now have a stable set of prev, middle, next VMAs threaded through
vmg and with these flags set know what is happening, we can perform the
calculation in commit_merge() instead.
This allows us to drop the confusing adj_start parameter and instead pass
semantic information to commit_merge().
In the latter case the -(middle->vm_end - start) calculation becomes
-(middle->vm-end - vmg->end), however this is correct as vmg->end is set
to the start parameter.
This is because in this case (rather confusingly), we manipulate
vmg->middle, but ultimately return vmg->next, whose range will be
correctly specified. At this point vmg->start, end is the new range for
the prior VMA rather than the merged one.
This patch has no change in functional behaviour.
Link: https://lkml.kernel.org/r/bcec0cd980b373a5eb02236cb033034ce1effe42.1738326519.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/vma.c')
| -rw-r--r-- | mm/vma.c | 50 |
1 files changed, 30 insertions, 20 deletions
diff --git a/mm/vma.c b/mm/vma.c index dd9fdf5c9429f6..bac0e72ccb6294 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -632,29 +632,44 @@ void validate_mm(struct mm_struct *mm) * * On success, returns the merged VMA. Otherwise returns NULL. */ -static struct vm_area_struct *commit_merge(struct vma_merge_struct *vmg, - long adj_start) +static struct vm_area_struct *commit_merge(struct vma_merge_struct *vmg) { - struct vma_prepare vp; struct vm_area_struct *remove = NULL; struct vm_area_struct *remove2 = NULL; + struct vma_prepare vp; struct vm_area_struct *adjust = NULL; + long adj_start; + bool merge_target; + /* - * In all cases but that of merge right, shrink next, we write - * vmg->target to the maple tree and return this as the merged VMA. + * If modifying an existing VMA and we don't remove vmg->middle, then we + * shrink the adjacent VMA. */ - bool merge_target = adj_start >= 0; + if (vmg->__adjust_middle_start) { + adjust = vmg->middle; + /* The POSITIVE value by which we offset vmg->middle->vm_start. */ + adj_start = vmg->end - vmg->middle->vm_start; + merge_target = true; + } else if (vmg->__adjust_next_start) { + adjust = vmg->next; + /* The NEGATIVE value by which we offset vmg->next->vm_start. */ + adj_start = -(vmg->middle->vm_end - vmg->end); + /* + * In all cases but this - merge right, shrink next - we write + * vmg->target to the maple tree and return this as the merged VMA. + */ + merge_target = false; + } else { + adjust = NULL; + adj_start = 0; + merge_target = true; + } if (vmg->__remove_middle) remove = vmg->middle; if (vmg->__remove_next) remove2 = vmg->next; - if (adj_start > 0) - adjust = vmg->middle; - else if (adj_start < 0) - adjust = vmg->next; - init_multi_vma_prep(&vp, vmg->target, adjust, remove, remove2); VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma && @@ -738,7 +753,6 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( bool left_side = middle && start == middle->vm_start; bool right_side = middle && end == middle->vm_end; int err = 0; - long adj_start = 0; bool merge_left, merge_right, merge_both; mmap_assert_write_locked(vmg->mm); @@ -858,11 +872,8 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( vmg->start = prev->vm_start; vmg->pgoff = prev->vm_pgoff; - /* - * We both expand prev and shrink middle. - */ if (!vmg->__remove_middle) - adj_start = vmg->end - middle->vm_start; + vmg->__adjust_middle_start = true; err = dup_anon_vma(prev, middle, &anon_dup); } else { /* merge_right */ @@ -891,12 +902,11 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( * IMPORTANT: This is the ONLY case where the final * merged VMA is NOT vmg->target, but rather vmg->next. */ + vmg->__adjust_next_start = true; vmg->target = middle; vmg->start = middle->vm_start; vmg->end = start; vmg->pgoff = middle->vm_pgoff; - - adj_start = -(middle->vm_end - start); } err = dup_anon_vma(next, middle, &anon_dup); @@ -905,7 +915,7 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( if (err) goto abort; - res = commit_merge(vmg, adj_start); + res = commit_merge(vmg); if (!res) { if (anon_dup) unlink_anon_vmas(anon_dup); @@ -1079,7 +1089,7 @@ int vma_expand(struct vma_merge_struct *vmg) if (remove_next) vmg->__remove_next = true; - if (!commit_merge(vmg, 0)) + if (!commit_merge(vmg)) goto nomem; return 0; |