On 7/3/19 10:37 AM, Michal Hocko wrote: > On Wed 03-07-19 09:12:13, Waiman Long wrote: >> On 7/3/19 2:56 AM, Michal Hocko wrote: >>> On Tue 02-07-19 14:37:30, Waiman Long 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 do we need a new value for this functionality? I would tend to think >>> that skipping memcg caches is a bug/incomplete implementation. Or is it >>> a deliberate decision to cover root caches only? >> It is just that I don't want to change the existing behavior of the >> current code. It will definitely take longer to shrink both the root >> cache and the memcg caches. > Does that matter? To whom and why? I do not expect this interface to be > used heavily. The only concern that I can see is the fact that I need to take the slab_mutex when iterating the memcg list to prevent concurrent modification. That may have some impact on other applications running in the system. However, I can put a precaution statement on the user-doc to discuss the potential performance impact. >> If we all agree that the only sensible >> operation is to shrink root cache and the memcg caches together. I am >> fine just adding memcg shrink without changing the sysfs interface >> definition and be done with it. > The existing documentation is really modest on the actual semantic: > Description: > The shrink file is written when memory should be reclaimed from > a cache. Empty partial slabs are freed and the partial list is > sorted so the slabs with the fewest available objects are used > first. > > which to me sounds like all slabs are free and nobody should be really > thinking of memcgs. This is simply drop_caches kinda thing. We surely do > not want to drop caches only for the root memcg for /proc/sys/vm/drop_caches > right? > I am planning to reword the document to make the effect of using this sysfs file more explicit. Cheers, Longman
