Re: [PATCH] mm, slab: Extend slab/shrink to shrink all the memcg caches

Waiman Long
2019-07-03T15:21:55Z

On 7/2/19 5:33 PM, Andrew Morton wrote:
> On Tue, 2 Jul 2019 16:44:24 -0400 Waiman Long <longman@redhat.com> wrote:
>
>> On 7/2/19 4:03 PM, Andrew Morton wrote:
>>> On Tue, 2 Jul 2019 14:37:30 -0400 Waiman Long <longman@redhat.com> wrote:
>>>
>>>> Currently, a value of '1" is written to /sys/kernel/slab/<slab>/shrink
>>>> file to shrink the slab by flushing all the per-cpu slabs and free
>>>> slabs in partial lists. This applies only to the root caches, though.
>>>>
>>>> Extends this capability by shrinking all the child memcg caches and
>>>> the root cache when a value of '2' is written to the shrink sysfs file.
>>> Why?
>>>
>>> Please fully describe the value of the proposed feature to or users.
>>> Always.
>> Sure. Essentially, the sysfs shrink interface is not complete. It allows
>> the root cache to be shrunk, but not any of the memcg caches.
> But that doesn't describe anything of value. Who wants to use this,
> and why? How will it be used? What are the use-cases?
>
For me, the primary motivation of posting this patch is to have a way to
make the number of active objects reported in /proc/slabinfo more
accurately reflect the number of objects that are actually being used by
the kernel. When measuring changes in slab objects consumption between
successive run of a certain workload, I can more easily see the amount
of increase. Without that, the data will have much more noise and it
will be harder to see a pattern.

Cheers,
Longman