linux-kernel - Re: THP: AnonHugePages in /proc/[pid]/smaps is correct or not?

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Message-ID: <515A5506.1000809@redhat.com>
Date:	Tue, 02 Apr 2013 11:48:22 +0800
From:	Zhouping Liu <zliu@...hat.com>
To:	Lin Feng <linfeng@...fujitsu.com>
CC:	David Rientjes <rientjes@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Amos Kong <akong@...hat.com>
Subject: Re: THP: AnonHugePages in /proc/[pid]/smaps is correct or not?

On 04/02/2013 11:40 AM, Lin Feng wrote:
> Hi Zhouping,
>
> On 04/02/2013 11:09 AM, Zhouping Liu wrote:
>> I don't understand clearly the last sentence 'you'll probably only get 100% hugepages only 1/512th of the time.'
>> could you please explain more details about 'only 1/512th of the time'?
> IIUC, thp size is 2M so it may be comprised of 512 normal page(size 4k).
> Since your test code is not 2M aligned(not using  posix_memalign()) so
> the start address of the mapped vma will be random, such as
> 2M*i+4k*1, 2M*i+4k*2...2M*i+k4*511, there is 512 possibilities.
>
> The only chance you get thp happens when the first map just starts at 2M*i,
> and the consequent maps also benefit from this.

Feng, it's easy to understand now, thanks for your detailed explanation :)

Zhouping
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