+ mmap-avoid-merging-cloned-vmas.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     mmap: avoid merging cloned VMAs
has been added to the -mm tree.  Its filename is
     mmap-avoid-merging-cloned-vmas.patch

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out what to do about this

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------------------------------------------------------
Subject: mmap: avoid merging cloned VMAs
From: Shaohua Li <shaohua.li@intel.com>

Avoid merging a VMA with another VMA which is cloned from the parent process.

The cloned VMA shares the anon_vma lock with the parent process's VMA.  If
we do the merge, more vmas (even the new range is only for current
process) use the perent process's anon_vma lock.  This introduces
scalability issues.  find_mergeable_anon_vma() already considers this
case.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mmap.c |   18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff -puN mm/mmap.c~mmap-avoid-merging-cloned-vmas mm/mmap.c
--- a/mm/mmap.c~mmap-avoid-merging-cloned-vmas
+++ a/mm/mmap.c
@@ -699,9 +699,17 @@ static inline int is_mergeable_vma(struc
 }
 
 static inline int is_mergeable_anon_vma(struct anon_vma *anon_vma1,
-					struct anon_vma *anon_vma2)
+					struct anon_vma *anon_vma2,
+					struct vm_area_struct *vma)
 {
-	return !anon_vma1 || !anon_vma2 || (anon_vma1 == anon_vma2);
+	/*
+	 * The list_is_singular() test is to avoid merging VMA cloned from
+	 * parents. This can improve scalability caused by anon_vma lock.
+	 */
+	if ((!anon_vma1 || !anon_vma2) && (!vma ||
+		list_is_singular(&vma->anon_vma_chain)))
+		return 1;
+	return anon_vma1 == anon_vma2;
 }
 
 /*
@@ -720,7 +728,7 @@ can_vma_merge_before(struct vm_area_stru
 	struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)
 {
 	if (is_mergeable_vma(vma, file, vm_flags) &&
-	    is_mergeable_anon_vma(anon_vma, vma->anon_vma)) {
+	    is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
 		if (vma->vm_pgoff == vm_pgoff)
 			return 1;
 	}
@@ -739,7 +747,7 @@ can_vma_merge_after(struct vm_area_struc
 	struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)
 {
 	if (is_mergeable_vma(vma, file, vm_flags) &&
-	    is_mergeable_anon_vma(anon_vma, vma->anon_vma)) {
+	    is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
 		pgoff_t vm_pglen;
 		vm_pglen = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
 		if (vma->vm_pgoff + vm_pglen == vm_pgoff)
@@ -817,7 +825,7 @@ struct vm_area_struct *vma_merge(struct 
 				can_vma_merge_before(next, vm_flags,
 					anon_vma, file, pgoff+pglen) &&
 				is_mergeable_anon_vma(prev->anon_vma,
-						      next->anon_vma)) {
+						      next->anon_vma, NULL)) {
 							/* cases 1, 6 */
 			err = vma_adjust(prev, prev->vm_start,
 				next->vm_end, prev->vm_pgoff, NULL);
_

Patches currently in -mm which might be from shaohua.li@intel.com are

origin.patch
mmap-avoid-unnecessary-anon_vma-lock.patch
mmap-avoid-merging-cloned-vmas.patch
mm-batch-activate_page-to-reduce-lock-contention.patch