From: Prasanna Meda <pmeda@akamai.com>
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>
---
25-akpm/mm/madvise.c | 27 ++++++++++++++++-----------
1 files changed, 16 insertions(+), 11 deletions(-)
diff -puN mm/madvise.c~madvise-do-not-split-the-maps mm/madvise.c
--- 25/mm/madvise.c~madvise-do-not-split-the-maps 2005-03-16 17:11:00.000000000 -0800
+++ 25-akpm/mm/madvise.c 2005-03-16 17:11:00.000000000 -0800
@@ -19,6 +19,21 @@ static long madvise_behavior(struct vm_a
{
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_a
* 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)
_