linux-kernel - Re: [bug, 4.8] /proc/meminfo: counter values are very wrong

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Date:	Fri, 5 Aug 2016 11:54:17 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Dave Chinner <david@...morbit.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [bug, 4.8] /proc/meminfo: counter values are very wrong

On Fri, Aug 05, 2016 at 09:11:10AM +1000, Dave Chinner wrote:
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index fb975cec3518..baa97da3687d 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -4064,7 +4064,7 @@ long si_mem_available(void)
> >  	int lru;
> >  
> >  	for (lru = LRU_BASE; lru < NR_LRU_LISTS; lru++)
> > -		pages[lru] = global_page_state(NR_LRU_BASE + lru);
> > +		pages[lru] = global_node_page_state(NR_LRU_BASE + lru);
> >  
> >  	for_each_zone(zone)
> >  		wmark_low += zone->watermark[WMARK_LOW];
> 
> OK, that makes the /proc accounting match the /sys per-node
> accounting, but the output still looks wrong. I remove files with
> cached pages from the filesystem (i.e. invalidate and free them),
> yet they are apparrently still accounted as being on the
> active/inactive LRU.
> 
> Reboot, then run dbench for a minute:
> 
> $ sudo mkfs.xfs -f /dev/pmem1
> meta-data=/dev/pmem1             isize=512    agcount=4, agsize=524288 blks
>          =                       sectsz=4096  attr=2, projid32bit=1
>          =                       crc=1        finobt=1, sparse=0
> data     =                       bsize=4096   blocks=2097152, imaxpct=25
>          =                       sunit=0      swidth=0 blks
> naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
> log      =internal log           bsize=4096   blocks=2560, version=2
>          =                       sectsz=4096  sunit=1 blks, lazy-count=1
> realtime =none                   extsz=4096   blocks=0, rtextents=0
> $ sudo mount /dev/pmem1 /mnt/scratch
> $ sudo dbench -t 60 -D /mnt/scratch/ 16
> dbench version 4.00 - Copyright Andrew Tridgell 1999-2004
> 

Is there any chance this is related to pmem1?

I tried reproducing this with the patch applied and free -m over time
looks like this

             total       used       free     shared    buffers     cached
# while [ 1 ]; do free -m | grep Mem; sleep 5; done
Mem:         15878        259      15618          1         12        123
Mem:         15878        274      15603          1         16        131
Mem:         15878        612      15266          1         17        463
Mem:         15878        617      15261          1         18        470
Mem:         15878        613      15265          1         19        463
Mem:         15878        614      15264          1         19        464
Mem:         15878        647      15231          1         20        498
Mem:         15878        616      15262          1         21        465
Mem:         15878        642      15236          1         22        491
Mem:         15878        618      15260          1         23        465
Mem:         15878        619      15259          1         24        466
Mem:         15878        620      15258          1         25        464
Mem:         15878        620      15257          1         26        466
Mem:         15878        622      15256          1         27        464
Mem:         15878        622      15255          1         27        466
Mem:         15878        285      15592          1         28        132
Mem:         15878        285      15592          1         28        132

Used memory before and after the dbench run were roughly similar

-- 
Mel Gorman
SUSE Labs