linux-kernel - Re: [PATCH v2 1/2] mm/rmap: fix and simplify reusing mergeable anon

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Message-ID: <20200118140029.z24bye6kq2yo33fn@master>
Date:   Sat, 18 Jan 2020 14:00:29 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        Li Xinhai <lixinhai.lxh@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        akpm <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rik van Riel <riel@...hat.com>,
        "kirill.shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v2 1/2] mm/rmap: fix and simplify reusing mergeable
 anon_vma as parent when fork

On Sat, Jan 18, 2020 at 11:04:21AM +0300, Konstantin Khlebnikov wrote:
>On 15/01/2020 04.20, Wei Yang wrote:
>> On Tue, Jan 14, 2020 at 10:42:52PM +0800, Li Xinhai wrote:
>> > On 2020-01-13??at 19:07??Konstantin Khlebnikov??wrote:
>> > 
>> > > 
>> > > Because I want to keep both heuristics.
>> > > This seems most sane way of interaction between them.
>> > > 
>> > > Unfortunately even this patch is slightly broken.
>> > > Condition prev->anon_vma->parent == pvma->anon_vma doesn't guarantee that
>> > > prev vma has the same set of anon-vmas like current vma.
>> > > I.e. anon_vma_clone(vma, prev) might be not enough for keeping connectivity.
>> > 
>> > New patch is required?
>> 
>> My suggestion is separate the fix and new approach instead of mess them into
>> one patch.
>
>Yep, it's messy. Maybe it's could be better to revert recent change,
>apply second patch from this set and write something new after that.
>

It is up to you.

>> 
>> > It is necessary to call anon_vma_clone(vma,??pvma) to link all anon_vma which
>> > currently linked by pvma, then link the prev->anon_vma to vma. By this way,
>> > connectivity of vma should be maintained, right?
>> > 
>> > > Building such case isn't trivial job but I see nothing that could prevent it.
>> > > 
>> > 
>> 

-- 
Wei Yang
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