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

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Date:   Tue, 11 Jul 2017 15:14:27 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...nel.org>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     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 11:56 AM, 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?

I believe removing this function is responsible for the
increase in speed of the test execution.