diff options
| author | Shaohua Li | 2011-05-24 17:11:20 -0700 |
|---|---|---|
| committer | Linus Torvalds | 2011-05-25 08:39:04 -0700 |
| commit | 965f55dea0e331152fa53941a51e4e16f9f06fae (patch) | |
| tree | 3cf8beb31bac7b325b62e8ef75618e0086a3c760 | |
| parent | 5f70b962ccc2f2e6259417cf3d1233dc9e16cf5e (diff) | |
mmap: avoid merging cloned VMAs
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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | mm/mmap.c | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/mm/mmap.c b/mm/mmap.c index 15b1fae57efe..4fb5464f7707 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -703,9 +703,17 @@ static inline int is_mergeable_vma(struct vm_area_struct *vma, } 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; } /* @@ -724,7 +732,7 @@ can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags, 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; } @@ -743,7 +751,7 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags, 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) @@ -821,7 +829,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm, 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); |