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

[Konstantin Khorenko]

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?

>> However free output was changed some time ago and this old issue is not actual now.
>> https://gitlab.com/procps-ng/procps/commit/2f96eef7f86a12b81badef1c91ec2d503ae4029d
>> library: reverting tmpfs subtraction from cached (18-FEB-2014)
>>
>> Therefore we're going to revert patch for previous issue
>> and believe that it resolves current problem too.
>>
>> https://jira.sw.ru/browse/PSBM-42024
>> Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
>>
>>
>