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

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Message-ID: <20170711065030.GE24852@dhcp22.suse.cz>
Date:   Tue, 11 Jul 2017 08:50:30 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     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 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.

-- 
Michal Hocko
SUSE Labs