mm/mmap: Combine multiple if statements in vma_merge()

Currently vma_merge() searches from 0 upwards if there is no prev vma,
or from prev->vm_end if there is a prev vma.  The check for merging with
prev also checks if prev exists.  The ordering is not important at this
stage, so move the merging check above finding the next vma so that prev
can be checked only once.

Also start searching from vma_start as apposed to 0.  If there is no
previous then there won't be a vma before vma_start.  The code reads
more clearly this way.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>

diff --git a/mm/mmap.c b/mm/mmap.c
index 97a422165a9adf6a84f766ca01291ea73090d66d..d39d71cbc0acee925d4b4f8d175b2cda886bc187 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -903,7 +903,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
        unsigned long vma_end = end;
        long adj_next = 0;
        unsigned long vma_start = addr;
-       MA_STATE(mas, &mm->mm_mt, 0, 0);
+       MA_STATE(mas, &mm->mm_mt, vma_start, vma_start);
 
        validate_mm(mm);
        /*
@@ -913,17 +913,8 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
        if (vm_flags & VM_SPECIAL)
                return NULL;
 
-       next = find_vma(mm, prev ? prev->vm_end : 0);
-       mid = next;
-       if (next && next->vm_end == end)                /* cases 6, 7, 8 */
-               next = find_vma(mm, next->vm_end);
-
-       /* verify some invariant that must be enforced by the caller */
-       VM_WARN_ON(prev && addr <= prev->vm_start);
-       VM_WARN_ON(mid && end > mid->vm_end);
-       VM_WARN_ON(addr >= end);
-
        if (prev) {
+               mas_set(&mas, prev->vm_end);
                res = prev;
                vma = prev;
                vma_start = prev->vm_start;
@@ -935,6 +926,17 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
                        merge_prev = true;
                }
        }
+
+       next = mas_find(&mas, end);
+       mid = next;
+       if (mid && mid->vm_end == end)          /* cases 6, 7, 8 */
+               next = mas_find(&mas, end);
+
+       /* verify some invariant that must be enforced by the caller */
+       VM_WARN_ON(prev && addr <= prev->vm_start);
+       VM_WARN_ON(mid && end > mid->vm_end);
+       VM_WARN_ON(addr >= end);
+
        /* Can we merge the successor? */
        if (next && end == next->vm_start &&
                        mpol_equal(policy, vma_policy(next)) &&