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

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Date:	Fri, 21 Aug 2015 08:32:33 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jörn Engel <joern@...estorage.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 Thu 20-08-15 12:49:59, David Rientjes wrote:
> On Thu, 20 Aug 2015, Michal Hocko wrote:
> 
> > On Thu 20-08-15 08:26:27, Naoya Horiguchi wrote:
> > > Currently there's no easy way to get per-process usage of hugetlb pages,
> > 
> > Is this really the case after your previous patch? You have both 
> > HugetlbPages and KernelPageSize which should be sufficient no?
> > 
> > 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?
> > 
> 
> /proc/pid/smaps requires root, /proc/pid/status doesn't.

Both mmotm and linus tree have
        REG("smaps",      S_IRUGO, proc_pid_smaps_operations),

and opening the file requires PTRACE_MODE_READ. So I do not see any
requirement for root here. Or did you mean that you need root to examine
all processes? That would be true but I am wondering why would be a regular
user interested in this break out numbers. Hugetlb management sounds
pretty much like an administrative or very specialized thing.

>From my understanding of the discussion there is no usecase to have this
information world readable. Is this correct?
-- 
Michal Hocko
SUSE Labs
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