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

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Message-ID: <4c182da0-6c84-df67-b173-6960fac0544a@suse.cz>
Date:   Tue, 11 Jul 2017 08:26:40 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     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 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?