The patch titled
Subject: mm/rmap.c: reuse mergeable anon_vma as parent when fork
has been added to the -mm tree. Its filename is
mm-rmapc-reuse-mergeable-anon_vma-as-parent-when-fork.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-rmapc-reuse-mergeable-anon_vma-as-parent-when-fork.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-rmapc-reuse-mergeable-anon_vma-as-parent-when-fork.patch
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------------------------------------------------------
From: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
Subject: mm/rmap.c: reuse mergeable anon_vma as parent when fork
In __anon_vma_prepare(), we will try to find anon_vma if it is possible to
reuse it. While on fork, the logic is different.
Since commit 5beb49305251 ("mm: change anon_vma linking to fix
multi-process server scalability issue"), function anon_vma_clone() tries
to allocate new anon_vma for child process. But the logic here will
allocate a new anon_vma for each vma, even in parent this vma is mergeable
and share the same anon_vma with its sibling. This may do better for
scalability issue, while it is not necessary to do so especially after
interval tree is used.
Commit 7a3ef208e662 ("mm: prevent endless growth of anon_vma hierarchy")
tries to reuse some anon_vma by counting child anon_vma and attached vmas.
While for those mergeable anon_vmas, we can just reuse it and not
necessary to go through the logic.
After this change, kernel build test reduces 20% anon_vma allocation.
Do the same kernel build test, it shows run time in sys reduced 11.6%.
Origin:
real 2m50.467s
user 17m52.002s
sys 1m51.953s
real 2m48.662s
user 17m55.464s
sys 1m50.553s
real 2m51.143s
user 17m59.687s
sys 1m53.600s
Patched:
real 2m39.933s
user 17m1.835s
sys 1m38.802s
real 2m39.321s
user 17m1.634s
sys 1m39.206s
real 2m39.575s
user 17m1.420s
sys 1m38.845s
Link: http://lkml.kernel.org/r/20191011072256.16275-2-richardw.yang@xxxxxxxxxxxxxxx
Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
Acked-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: "Jérôme Glisse" <jglisse@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Qian Cai <cai@xxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/rmap.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
--- a/mm/rmap.c~mm-rmapc-reuse-mergeable-anon_vma-as-parent-when-fork
+++ a/mm/rmap.c
@@ -268,6 +268,19 @@ int anon_vma_clone(struct vm_area_struct
{
struct anon_vma_chain *avc, *pavc;
struct anon_vma *root = NULL;
+ struct vm_area_struct *prev = dst->vm_prev, *pprev = src->vm_prev;
+
+ /*
+ * If parent share anon_vma with its vm_prev, keep this sharing in in
+ * child.
+ *
+ * 1. Parent has vm_prev, which implies we have vm_prev.
+ * 2. Parent and its vm_prev have the same anon_vma.
+ */
+ if (!dst->anon_vma && src->anon_vma &&
+ pprev && pprev->anon_vma == src->anon_vma)
+ dst->anon_vma = prev->anon_vma;
+
list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
struct anon_vma *anon_vma;
_
Patches currently in -mm which might be from richardw.yang@xxxxxxxxxxxxxxx are
mm-mmapc-remove-a-never-trigger-warning-in-__vma_adjust.patch
mm-mmapc-prev-could-be-retrieved-from-vma-vm_prev.patch
mm-mmapc-__vma_unlink_prev-is-not-necessary-now.patch
mm-mmapc-extract-__vma_unlink_list-as-counter-part-for-__vma_link_list.patch
mm-mmapc-rb_parent-is-not-necessary-in-__vma_link_list.patch
mm-rmapc-dont-reuse-anon_vma-if-we-just-want-a-copy.patch
mm-rmapc-reuse-mergeable-anon_vma-as-parent-when-fork.patch
hugetlb-remove-unused-hstate-in-hugetlb_fault_mutex_hash.patch
userfaultfd-use-vma_pagesize-for-all-huge-page-size-calculation.patch
userfaultfd-remove-unnecessary-warn_on-in-__mcopy_atomic_hugetlb.patch
userfaultfd-wrap-the-common-dst_vma-check-into-an-inlined-function.patch
mm-fix-typo-in-the-comment-when-calling-function-__setpageuptodate.patch
