Re: [PATCH 2/2] mm, slab: Extend vm/drop_caches to shrink kmem slabs

From: Waiman Long
Date: Thu Jun 27 2019 - 17:32:28 EST

On 6/27/19 5:24 PM, Roman Gushchin wrote:
>>> 2) what's your long-term vision here? do you think that we need to shrink
>>> kmem_caches periodically, depending on memory pressure? how a user
>>> will use this new sysctl?
>> Shrinking the kmem caches under extreme memory pressure can be one way
>> to free up extra pages, but the effect will probably be temporary.
>>> What's the problem you're trying to solve in general?
>> At least for the slub allocator, shrinking the caches allow the number
>> of active objects reported in slabinfo to be more accurate. In addition,
>> this allow to know the real slab memory consumption. I have been working
>> on a BZ about continuous memory leaks with a container based workloads.
>> The ability to shrink caches allow us to get a more accurate memory
>> consumption picture. Another alternative is to turn on slub_debug which
>> will then disables all the per-cpu slabs.
> I see... I agree with Michal here, that extending drop_caches sysctl isn't
> the best idea. Isn't it possible to achieve the same effect using slub sysfs?

Yes, using the slub sysfs interface can be a possible alternative.