linux-kernel - Re: [PATCH v5 2/2] mm: hugetlb: proc: add HugetlbPages field to /proc/PID/status

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Date:	Mon, 24 Aug 2015 10:51:27 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Jörn Engel <joern@...estorage.com>
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Mike Kravetz <mike.kravetz@...cle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH v5 2/2] mm: hugetlb: proc: add HugetlbPages field to
 /proc/PID/status

On Fri 21-08-15 09:30:33, Jörn Engel wrote:
> On Fri, Aug 21, 2015 at 08:53:21AM +0200, Michal Hocko wrote:
> > On Thu 20-08-15 23:34:51, Naoya Horiguchi wrote:
> > [...]
> > > > Reading a single file is, of course, easier but is it really worth the
> > > > additional code? I haven't really looked at the patch so I might be
> > > > missing something but what would be an advantage over reading
> > > > /proc/<pid>/smaps and extracting the information from there?
> > > 
> > > My first idea was just "users should feel it useful", but permission as David
> > > commented sounds a good technical reason to me.
> > 
> > 9 files changed, 112 insertions(+), 1 deletion(-)
> > 
> > is quite a lot especially when it touches hot paths like fork so it
> > better should have a good usecase. I have already asked in the other
> > email but is actually anybody requesting this? Nice to have is not
> > a good justification IMO.
> 
> I need some way to judge the real rss of a process, including huge
> pages.  No strong opinion on implementation details, but something is
> clearly needed.

The current implementation makes me worry. Is the per hstate break down
really needed? The implementation would be much more easier without it.

> If you have processes with 99% huge pages, you are currently reduced to
> guesswork.

If you have 99% of hugetlb pages then your load is rather specific and I
would argue that /proc/<pid>/smaps (after patch 1) is a much better way to
get what you want.

-- 
Michal Hocko
SUSE Labs
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