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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 5beb493052 ("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 7a3ef208e6 ("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@linux.intel.com
Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Acked-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Wei Yang 2019-11-30 17:50:59 -08:00 committed by Linus Torvalds
parent 47b390d23b
commit 4e4a9eb921
1 changed files with 13 additions and 0 deletions
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13
mm/rmap.c
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@ -269,6 +269,19 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
{
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;