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

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Date:	Mon, 1 Apr 2013 20:44:34 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Lin Feng <linfeng@...fujitsu.com>
cc:	Zhouping Liu <zliu@...hat.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 Tue, 2 Apr 2013, Lin Feng wrote:

> > so, again, if I understand correctly, thp should tune the naturally aligned maps, such as generated by mmap()/malloc(),
> > make such maps 'hugepagesize' aligned if the maps or vma is equal and greater than 'hugepagesize', doesn't it?
> 
> We may gain performance improving from this.
> 

To attain the maximum number of hugepages, you would naturally want to 
ensure that the mappings are done aligned to 2MB; for very large 
allocations, missing one or two hugepages typically won't hurt performance 
much.  posix_memalign() is the best way of doing this which just wraps 
mmap() for the needed alignment.  More interesting is creating your own 
custom malloc() that allocates in 2MB aligned chunks, if possible, and 
uses 2MB aligned arenas for its own metadata.  If you do that for 
malloc(), then you'll only need to make code that does its own mmap()s to 
use posix_memalign().
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