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mm/vma: clean up anon_vma_compatible()

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Break up the existing very large conditional, add comments and use
vma_[start/end]_pgoff() to make clearer what we're doing here.

No functional change intended.

Link: https://lore.kernel.org/20260710-b4-pre-scalable-cow-v2-14-2a5aa403d977@kernel.org
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Kai Huang <kai.huang@intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: SJ Park <sj@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Liam R. Howlett (Oracle) <liam@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Lorenzo Stoakes
2026-07-10 21:16:55 +01:00
committed by Andrew Morton
parent 8802c4069e
commit dfe2b9abf6
1 changed files with 16 additions and 5 deletions
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21
mm/vma.c
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@@ -1967,14 +1967,25 @@ static int anon_vma_compatible(struct vm_area_struct *a, struct vm_area_struct *
{
vma_flags_t diff = vma_flags_diff_pair(&a->flags, &b->flags);
/* Ignore flags that mprotect() can change. */
vma_flags_clear_mask(&diff, VMA_ACCESS_FLAGS);
/* Ignore flags that do not impact merging. */
vma_flags_clear_mask(&diff, VMA_IGNORE_MERGE_FLAGS);
return a->vm_end == b->vm_start &&
mpol_equal(vma_policy(a), vma_policy(b)) &&
a->vm_file == b->vm_file &&
vma_flags_empty(&diff) &&
b->vm_pgoff == a->vm_pgoff + ((b->vm_start - a->vm_start) >> PAGE_SHIFT);
/* Must be adjacent. */
if (a->vm_end != b->vm_start)
return false;
/* Must have matching policy. */
if (!mpol_equal(vma_policy(a), vma_policy(b)))
return false;
/* Must both be anon or map the same file (MAP_PRIVATE case). */
if (a->vm_file != b->vm_file)
return false;
/* Flags must be equivalent modulo mprotect(). */
if (!vma_flags_empty(&diff))
return false;
/* Page offset must align. */
return vma_end_pgoff(a) == vma_start_pgoff(b);
}
/*