[PATCH] madvise: do not split the maps

This attempts to avoid splittings when it is not needed, that is when
vm_flags are same as new flags.  The idea is from the <2.6.11 mlock_fixup
and others.  This will provide base for the next madvise merging patch.

Signed-off-by: Prasanna Meda <pmeda@akamai.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 16 insertions, 11 deletions

diff --git a/mm/madvise.c b/mm/madvise.c
index 944b5e52d812..75b81ad1f98c 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -19,6 +19,21 @@ static long madvise_behavior(struct vm_area_struct * vma, unsigned long start,
 {
         struct mm_struct * mm = vma->vm_mm;
         int error = 0;
+        int new_flags = vma->vm_flags & ~VM_READHINTMASK;
+
+        switch (behavior) {
+        case MADV_SEQUENTIAL:
+                new_flags |= VM_SEQ_READ;
+                break;
+        case MADV_RANDOM:
+                new_flags |= VM_RAND_READ;
+                break;
+        default:
+                break;
+        }
+
+        if (new_flags == vma->vm_flags)
+                goto out;
 
         if (start != vma->vm_start) {
                 error = split_vma(mm, vma, start, 1);
@@ -36,17 +51,7 @@ static long madvise_behavior(struct vm_area_struct * vma, unsigned long start,
          * vm_flags is protected by the mmap_sem held in write mode.
          */
         VM_ClearReadHint(vma);
-
-        switch (behavior) {
-        case MADV_SEQUENTIAL:
-                vma->vm_flags |= VM_SEQ_READ;
-                break;
-        case MADV_RANDOM:
-                vma->vm_flags |= VM_RAND_READ;
-                break;
-        default:
-                break;
-        }
+        vma->vm_flags = new_flags;
 
 out:
         if (error == -ENOMEM)