On 7/2/19 5:33 PM, Andrew Morton wrote:

On Tue, 2 Jul 2019 16:44:24 -0400 Waiman Long [off-list ref] wrote:

quoted

On 7/2/19 4:03 PM, Andrew Morton wrote:

quoted

On Tue,  2 Jul 2019 14:37:30 -0400 Waiman Long [off-list ref] wrote:

quoted

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