linux-kernel - Re: [RESEND [PATCH] 0/2] mm/mmap.c: reduce subtree gap propagation a little

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Message-ID: <20190828082738.GA20183@richard>
Date:   Wed, 28 Aug 2019 16:27:38 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        yang.shi@...ux.alibaba.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Matthew Wilcox <willy@...radead.org>
Subject: Re: [RESEND [PATCH] 0/2] mm/mmap.c: reduce subtree gap propagation a
 little

On Wed, Aug 28, 2019 at 10:01:40AM +0200, Vlastimil Babka wrote:
>On 8/28/19 8:06 AM, Wei Yang wrote:
>> When insert and delete a vma, it will compute and propagate related subtree
>> gap. After some investigation, we can reduce subtree gap propagation a little.
>> 
>> [1]: This one reduce the propagation by update *next* gap after itself, since
>>      *next* must be a parent in this case.
>> [2]: This one achieve this by unlinking vma from list.
>> 
>> After applying these two patches, test shows it reduce 0.3% function call for
>> vma_compute_subtree_gap.
>
>BTW, what's the overall motivation of focusing so much
>micro-optimization effort on the vma tree lately? This has been rather
>stable code where we can be reasonably sure of all bugs being found. Now
>even after some review effort, subtle bugs can be introduced. And
>Matthew was warning for a while about an upcoming major rewrite of the
>whole data structure, which will undo all this effort?
>

Hi, Vlastimil

Thanks for your comment.

I just found there could be some refine for the code and then I modify and
test it. Hope this could help a little.

You concern is valid. The benefits / cost may be not that impressive. The
community have the final decision. For me, I just want to make it better if we
can.

-- 
Wei Yang
Help you, Help me