linux-kernel - Re: [PATCH 0/3] mm: hugetlbfs: fix hugetlbfs optimization v2

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Message-ID: <528A56A7.3020301@oracle.com>
Date:	Mon, 18 Nov 2013 11:04:23 -0700
From:	Khalid Aziz <khalid.aziz@...cle.com>
To:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Pravin Shelar <pshelar@...ira.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ben Hutchings <bhutchings@...arflare.com>,
	Christoph Lameter <cl@...ux.com>,
	Johannes Weiner <jweiner@...hat.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Minchan Kim <minchan@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/3] mm: hugetlbfs: fix hugetlbfs optimization v2

On 11/15/2013 10:47 AM, Andrea Arcangeli wrote:
> Hi,
>
> 1/3 is a bugfix so it should be applied more urgently. 1/3 is not as
> fast as the current upstream code in the hugetlbfs + directio extreme
> 8GB/sec benchmark (but 3/3 should fill the gap later). The code is
> identical to the one I posted in v1 just rebased on upstream and was
> developed in collaboration with Khalid who already tested it.
>
> 2/3 and 3/3 had very little testing yet, and they're incremental
> optimization. 2/3 is minor and most certainly worth applying later.
>
> 3/3 instead complicates things a bit and adds more branches to the THP
> fast paths, so it should only be applied if the benchmarks of
> hugetlbfs + directio show that it is very worthwhile (that has not
> been verified yet). If it's not worthwhile 3/3 should be dropped (and
> the gap should be filled in some other way if the gap is not caused by
> the _mapcount mangling as I guessed). Ideally this should bring even
> more performance than current upstream code, as current upstream code
> still increased the _mapcount in gup_fast by mistake, while this
> eliminates the locked op on the tail page cacheline in gup_fast too
> (which is required for correctness too).

Hi Andrea,

I ran directio benchmark and here are the performance numbers (MBytes/sec):

Block size        3.12         3.12+patch 1      3.12+patch 1,2,3
----------        ----         ------------      ----------------
1M                8467           8114              7648
64K               4049           4043              4175

Performance numbers with 64K reads look good but there is further 
deterioration with 1M reads.

--
Khalid
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