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

On 6/27/19 5:24 PM, Roman Gushchin wrote:

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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.

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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.

Cheers,
Longman