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Subject: Re: [PATCH v2 1/2] mm/rmap: fix and simplify reusing mergeable
 anon_vma as parent when fork
To:     Wei Yang <richardw.yang@linux.intel.com>,
        Li Xinhai <lixinhai.lxh@gmail.com>
Cc:     "linux-mm@kvack.org" <linux-mm@kvack.org>,
        akpm <akpm@linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Rik van Riel <riel@redhat.com>,
        "kirill.shutemov" <kirill.shutemov@linux.intel.com>
References: <b8269278-85b5-9fd2-9bce-6defffcad6e8@yandex-team.ru>
 <20200110023029.GB16823@richard> <20200110112357351531132@gmail.com>
 <20200110053442.GA27846@richard>
 <d89587b7-f59f-3897-968b-969b946a9e8a@yandex-team.ru>
 <20200111223820.GA15506@richard>
 <a6a7bb3b-434e-277c-694f-d5a18e629d2c@yandex-team.ru>
 <20200113003343.GA27210@richard>
 <1cf002fa-a3cb-bcef-57dc-ac9c09dcf2eb@yandex-team.ru>
 <2020011422424965556826@gmail.com> <20200115012055.GC4916@richard>
From:   Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Message-ID: <8f335403-4a14-bd17-39da-6299dd962fc6@yandex-team.ru>
Date:   Sat, 18 Jan 2020 11:04:21 +0300
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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 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.
>>>
>>
>