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

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Date:	Tue, 25 Aug 2015 16:23:34 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Michal Hocko <mhocko@...nel.org>
cc:	Jörn Engel <joern@...estorage.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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 Mon, 24 Aug 2015, Michal Hocko wrote:

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

Yes, it's needed.  It provides a complete picture of what statically 
reserved hugepages are in use and we're not going to change the 
implementation when it is needed to differentiate between variable hugetlb 
page sizes that risk breaking existing userspace parsers.

> 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.
> 

Some distributions change the permissions of smaps, as already stated, for 
pretty clear security reasons since it can be used to defeat existing 
protection.  There's no reason why hugetlb page usage should not be 
exported in the same manner and location as memory usage.

Sheesh.
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