linux-kernel - RE: [PATCH] mm: export NR_SHMEM via sysinfo(2) / si

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Message-ID: <6B2BA408B38BA1478B473C31C3D2074E341D585503@SV-EXCHANGE1.Corp.FC.LOCAL>
Date:	Wed, 25 Jun 2014 13:27:53 -0700
From:	Motohiro Kosaki <Motohiro.Kosaki@...fujitsu.com>
To:	Rafael Aquini <aquini@...hat.com>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Motohiro Kosaki JP <kosaki.motohiro@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] mm: export NR_SHMEM via sysinfo(2) / si_meminfo()
 interfaces



> -----Original Message-----
> From: Rafael Aquini [mailto:aquini@...hat.com]
> Sent: Wednesday, June 25, 2014 4:16 PM
> To: Motohiro Kosaki
> Cc: linux-mm@...ck.org; Andrew Morton; Rik van Riel; Mel Gorman; Johannes Weiner; Motohiro Kosaki JP; linux-
> kernel@...r.kernel.org
> Subject: Re: [PATCH] mm: export NR_SHMEM via sysinfo(2) / si_meminfo() interfaces
> 
> On Wed, Jun 25, 2014 at 12:41:17PM -0700, Motohiro Kosaki wrote:
> >
> >
> > > -----Original Message-----
> > > From: Rafael Aquini [mailto:aquini@...hat.com]
> > > Sent: Wednesday, June 25, 2014 2:40 PM
> > > To: linux-mm@...ck.org
> > > Cc: Andrew Morton; Rik van Riel; Mel Gorman; Johannes Weiner;
> > > Motohiro Kosaki JP; linux-kernel@...r.kernel.org
> > > Subject: [PATCH] mm: export NR_SHMEM via sysinfo(2) / si_meminfo()
> > > interfaces
> > >
> > > This patch leverages the addition of explicit accounting for pages
> > > used by shmem/tmpfs -- "4b02108 mm: oom analysis: add shmem vmstat"
> > > -- in order to make the users of sysinfo(2) and si_meminfo*() friends aware of that vmstat entry consistently across the interfaces.
> >
> > Why?
> 
> Because we do not report consistently across the interfaces we declare exporting that data. Check sysinfo(2) manpage, for instance:
> [...]
>            struct sysinfo {
>                long uptime;             /* Seconds since boot */
>                unsigned long loads[3];  /* 1, 5, and 15 minute load averages */
>                unsigned long totalram;  /* Total usable main memory size */
>                unsigned long freeram;   /* Available memory size */
>                unsigned long sharedram; /* Amount of shared memory */ <<<<< [...]
> 
> userspace tools resorting to sysinfo() syscall will get a hardcoded 0 for shared memory which is reported differently from
> /proc/meminfo.
> 
> Also, si_meminfo() & si_meminfo_node() are utilized within the kernel to gather statistics for /proc/meminfo & friends, and so we
> can leverage collecting sharedmem from those calls as well, just as we do for totalram, freeram & bufferram.

But "Amount of shared memory"  didn't mean amout of shmem. It actually meant amout of page of page-count>=2.
Again, there is a possibility to change the semantics. But I don't have enough userland knowledge to do. Please investigate
and explain why your change don't break any userland. 






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