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Commit 965f55de authored by Shaohua Li's avatar Shaohua Li Committed by Linus Torvalds
Browse files

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: default avatarShaohua 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5f70b962

mm/mmap.c

+13 −5
Original line number Original line Diff line number Diff line
@@ -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,

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)

	struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)

{

{

	if (is_mergeable_vma(vma, file, vm_flags) &&

	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)

		if (vma->vm_pgoff == vm_pgoff)

			return 1;

			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)

	struct anon_vma *anon_vma, struct file *file, pgoff_t vm_pgoff)

{

{

	if (is_mergeable_vma(vma, file, vm_flags) &&

	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;

		pgoff_t vm_pglen;

		vm_pglen = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;

		vm_pglen = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;

		if (vma->vm_pgoff + vm_pglen == vm_pgoff)

		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,

				can_vma_merge_before(next, vm_flags,

					anon_vma, file, pgoff+pglen) &&

					anon_vma, file, pgoff+pglen) &&

				is_mergeable_anon_vma(prev->anon_vma,

				is_mergeable_anon_vma(prev->anon_vma,

						      next->anon_vma)) {

						      next->anon_vma, NULL)) {

							/* cases 1, 6 */

							/* cases 1, 6 */

			err = vma_adjust(prev, prev->vm_start,

			err = vma_adjust(prev, prev->vm_start,

				next->vm_end, prev->vm_pgoff, NULL);

				next->vm_end, prev->vm_pgoff, NULL);