[Devel] [patch rh7] free shows used=0 inside centos7 CT

[Vladimir Davydov]

On Tue, Feb 16, 2016 at 12:59:25PM +0300, Konstantin Khorenko wrote:
> On 02/09/2016 03:54 PM, Andrey Ryabinin wrote:
> >
> >
> >On 12/04/2015 08:16 PM, Vasily Averin wrote:
> >>Customer reports that free or top command inside Centos7 CT shows 0 memory used
> >>
> >>free from procps-ng-3.3.10-3.el7 uses /proc/meminfo output and calculates
> >>used = total - free - buffers - cache - slab
> >>
> >>However kernel in some cases calculates "Cached" value in meminfo output by using
> >>the same formula:
> >>cached = total - free - slab (where buffers = 0)
> >
> >So this is the actual problem. Whenever we use that formula the used calculated as
> >	used = total - free - buffers - cached - slab
> >means that
> >	used =  -buffers
> >And the patch do nothing about this. We still could get the this situation.
> >
> >>
> >>Alternative calculation of cached value does not work  this time becasue
> >>additional UB_SHMPAGES.held argument added to work-around
> >>"negative cached" problem in previous version of free/procps-ng
> >>see PSBM-29352 and http://kb.sp.parallels.com/en/123422
> >>
> >
> >It's not work-around, it's a correct bugfix. Shmem pages are accounted as "Cached".
> >So just removing it would make "Cached" value incorrect again.
> >
> >Probably we could solve this by reading 'cached' value from memcg stats (mem_cgroup_read_stat()).
> 
> Volodya, your opinion?

I think it's a good idea.