Re: [PATCH] mm: export NR_SHMEM via sysinfo(2) / si_meminfo() interfaces

[Rafael Aquini <aquini@redhat.com>]

On Wed, Jun 25, 2014 at 12:41:17PM -0700, Motohiro Kosaki wrote:
> 
> 
> > -----Original Message-----
> > From: Rafael Aquini [mailto:aquini@redhat.com]
> > Sent: Wednesday, June 25, 2014 2:40 PM
> > To: linux-mm@kvack.org
> > Cc: Andrew Morton; Rik van Riel; Mel Gorman; Johannes Weiner; Motohiro Kosaki JP; linux-kernel@vger.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.

Regards,
-- Rafael

> Traditionally sysinfo.sharedram was not used for shmem. It was totally strange semantics and completely outdated feature. 
> So, we may reuse it for another purpose. But I'm not sure its benefit. 
> 
> Why don't you use /proc/meminfo?
> I'm afraid userland programs get a confusion. 
> 
> 
> > 
> > Signed-off-by: Rafael Aquini <aquini@redhat.com>
> > ---
> >  drivers/base/node.c | 2 +-
> >  fs/proc/meminfo.c   | 2 +-
> >  mm/page_alloc.c     | 3 ++-
> >  3 files changed, 4 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/base/node.c b/drivers/base/node.c index 8f7ed99..c6d3ae0 100644
> > --- a/drivers/base/node.c
> > +++ b/drivers/base/node.c
> > @@ -126,7 +126,7 @@ static ssize_t node_read_meminfo(struct device *dev,
> >  		       nid, K(node_page_state(nid, NR_FILE_PAGES)),
> >  		       nid, K(node_page_state(nid, NR_FILE_MAPPED)),
> >  		       nid, K(node_page_state(nid, NR_ANON_PAGES)),
> > -		       nid, K(node_page_state(nid, NR_SHMEM)),
> > +		       nid, K(i.sharedram),
> >  		       nid, node_page_state(nid, NR_KERNEL_STACK) *
> >  				THREAD_SIZE / 1024,
> >  		       nid, K(node_page_state(nid, NR_PAGETABLE)), diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c index
> > 7445af0..aa1eee0 100644
> > --- a/fs/proc/meminfo.c
> > +++ b/fs/proc/meminfo.c
> > @@ -168,7 +168,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
> >  		K(global_page_state(NR_WRITEBACK)),
> >  		K(global_page_state(NR_ANON_PAGES)),
> >  		K(global_page_state(NR_FILE_MAPPED)),
> > -		K(global_page_state(NR_SHMEM)),
> > +		K(i.sharedram),
> >  		K(global_page_state(NR_SLAB_RECLAIMABLE) +
> >  				global_page_state(NR_SLAB_UNRECLAIMABLE)),
> >  		K(global_page_state(NR_SLAB_RECLAIMABLE)),
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 20d17f8..f72ea38 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -3040,7 +3040,7 @@ static inline void show_node(struct zone *zone)  void si_meminfo(struct sysinfo *val)  {
> >  	val->totalram = totalram_pages;
> > -	val->sharedram = 0;
> > +	val->sharedram = global_page_state(NR_SHMEM);
> >  	val->freeram = global_page_state(NR_FREE_PAGES);
> >  	val->bufferram = nr_blockdev_pages();
> >  	val->totalhigh = totalhigh_pages;
> > @@ -3060,6 +3060,7 @@ void si_meminfo_node(struct sysinfo *val, int nid)
> >  	for (zone_type = 0; zone_type < MAX_NR_ZONES; zone_type++)
> >  		managed_pages += pgdat->node_zones[zone_type].managed_pages;
> >  	val->totalram = managed_pages;
> > +	val->sharedram = node_page_state(nid, NR_SHMEM);
> >  	val->freeram = node_page_state(nid, NR_FREE_PAGES);  #ifdef CONFIG_HIGHMEM
> >  	val->totalhigh = pgdat->node_zones[ZONE_HIGHMEM].managed_pages;
> > --
> > 1.9.3
> 

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