linux-kernel - Re: [PATCHv7 00/29] THP-enabled tmpfs/shmem using compound pages

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Date:	Tue, 19 Apr 2016 16:33:16 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	"Shi, Yang" <yang.shi@...aro.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dave Hansen <dave.hansen@...el.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Andres Lagar-Cavilla <andreslc@...gle.com>,
	Ning Qu <quning@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCHv7 00/29] THP-enabled tmpfs/shmem using compound pages

On 04/19/2016 12:55 AM, Shi, Yang wrote:
> 2. I ran my THP test (generated a program with 4MB text section) on both
> x86-64 and ARM64 with yours and Hugh's patches (linux-next tree), I got
> the program execution time reduced by ~12% on x86-64, it looks very
> impressive.
> 
> But, on ARM64, there is just ~3% change, and sometimes huge tmpfs may
> show even worse data than non-hugepage.
> 
> Both yours and Hugh's patches has the same behavior.
> 
> Any idea?

Just a shot in the dark, but what page size do you use? If you use 4k
pages, then hugepage size should be the same as on x86 and a similar
behavior could be expected. Otherwise, hugepages would be too big to be
taken advantage of by your test program.

Jerome



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