The patch titled
Subject: mm/rmap.c: reuse mergeable anon_vma as parent when forking
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 forking
In function __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 and record time:
Original
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 2m43.733s
user 17m25.705s
sys 1m41.791s
real 2m47.146s
user 17m47.451s
sys 1m43.474s
real 2m45.763s
user 17m38.230s
sys 1m42.102s
System time is reduced by 8.5%.
Link: http://lkml.kernel.org/r/20191004160632.30251-1-richardw.yang@xxxxxxxxxxxxxxx
Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
Acked-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/rmap.c | 11 +++++++++++
1 file changed, 11 insertions(+)
--- a/mm/rmap.c~mm-rmapc-reuse-mergeable-anon_vma-as-parent-when-fork
+++ a/mm/rmap.c
@@ -262,6 +262,17 @@ 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 (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-fix-typo-in-the-comment-when-calling-function-__setpageuptodate.patch
mm-mmapc-remove-a-never-trigger-warning-in-__vma_adjust.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
