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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------------------------------------------------------
Subject: mmap: avoid merging cloned VMAs
From: Shaohua Li <shaohua.li@xxxxxxxxx>
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@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxx 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
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