Re: [PATCH] mm/rmap.c: reuse mergeable anon_vma as parent when fork

[Rik van Riel]

On Sat, 2019-10-05 at 00:06 +0800, Wei Yang wrote:
> 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.
> 
> Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>

Acked-by: Rik van Riel <riel@xxxxxxxxxxx>

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