Re: [RFC] mm/mremap: Remove redundant checks inside vma_expandable()

From: Anshuman Khandual
Date: Tue Jul 11 2017 - 05:45:55 EST

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.