Re: [PATCH] mm: slub: replace kick_all_cpus_sync with synchronize_sched in kmem_cache_shrink

[Peter Zijlstra]

On Fri, Apr 01, 2016 at 03:30:17PM +0300, Vladimir Davydov wrote:
> When we call __kmem_cache_shrink on memory cgroup removal, we need to
> synchronize kmem_cache->cpu_partial update with put_cpu_partial that
> might be running on other cpus. Currently, we achieve that by using
> kick_all_cpus_sync, which works as a system wide memory barrier. Though
> fast it is, this method has a flow - it issues a lot of IPIs, which
> might hurt high performance or real-time workloads.
> 
> To fix this, let's replace kick_all_cpus_sync with synchronize_sched.
> Although the latter one may take much longer to finish, it shouldn't be
> a problem in this particular case, because memory cgroups are destroyed
> asynchronously from a workqueue so that no user visible effects should
> be introduced. OTOH, it will save us from excessive IPIs when someone
> removes a cgroup.
> 
> Anyway, even if using synchronize_sched turns out to take too long, we
> can always introduce a kind of __kmem_cache_shrink batching so that this
> method would only be called once per one cgroup destruction (not per
> each per memcg kmem cache as it is now).
> 
> Reported-and-suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>

Thanks!

Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>