[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>
diff --git a/mm/madvise.c b/mm/madvise.c
index 944b5e5..75b81ad 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -19,6 +19,21 @@
{
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 @@
* 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)