linux-kernel - Re: [RFC] mm/mremap: Remove redundant checks inside vma

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Date:   Tue, 11 Jul 2017 16:36:40 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Michal Hocko <mhocko@...nel.org>, Vlastimil Babka <vbabka@...e.cz>
Cc:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, mike.kravetz@...cle.com
Subject: Re: [RFC] mm/mremap: Remove redundant checks inside vma_expandable()

On 07/11/2017 12:20 PM, Michal Hocko wrote:
> On Tue 11-07-17 08:26:40, Vlastimil Babka wrote:
>> On 07/11/2017 08:03 AM, Michal Hocko wrote:
>>> On Tue 11-07-17 09:58:42, Anshuman Khandual wrote:
>>>>> here. This is hardly something that would save many cycles in a
>>>>> relatively cold path.
>>>> Though I have not done any detailed instruction level measurement,
>>>> there is a reduction in real and system amount of time to execute
>>>> the test with and without the patch.
>>>>
>>>> Without the patch
>>>>
>>>> real	0m2.100s
>>>> user	0m0.162s
>>>> sys	0m1.937s
>>>>
>>>> With this patch
>>>>
>>>> real	0m0.928s
>>>> user	0m0.161s
>>>> sys	0m0.756s
>>> Are you telling me that two if conditions cause more than a second
>>> difference? That sounds suspicious.
>> It's removing also a call to get_unmapped_area(), AFAICS. That means a
>> vma search?
> Ohh, right. I have somehow missed that. Is this removal intentional? The
> changelog is silent about it.

Yeah it was.