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From:   Lorenzo Stoakes <lstoakes@gmail.com>
To:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     David Hildenbrand <david@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Liam R . Howlett" <Liam.Howlett@oracle.com>,
        maple-tree@lists.infradead.org, Vernon Yang <vernon2gm@gmail.com>,
        Lorenzo Stoakes <lstoakes@gmail.com>
Subject: [PATCH v3 2/4] mm/mmap/vma_merge: fold curr, next assignment logic
Date:   Wed, 22 Mar 2023 07:13:02 +0000
Message-Id: <36399b6cdc843eb7fe243488ea9b29464f699170.1679468982.git.lstoakes@gmail.com>
In-Reply-To: <cover.1679468982.git.lstoakes@gmail.com>
References: <cover.1679468982.git.lstoakes@gmail.com>
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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.

Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
---
 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);
+	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 &&
-			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