On Fri, May 30, 2014 at 10:01:26AM -0500, Christoph Lameter wrote: > On Fri, 30 May 2014, Vladimir Davydov wrote: > > > We don't disable free objects caching for SLAB, because it would force > > kfree to always take a spin lock, which would degrade performance > > significantly. > > You can use a similar approach than in SLUB. Reduce the size of the per > cpu array objects to zero. Then SLAB will always fall back to its slow > path in cache_flusharray() where you may be able to do something with less > of an impact on performace. In contrast to SLUB, for SLAB this will slow down kfree significantly. Fast path for SLAB is just putting an object to a per cpu array, while the slow path requires taking a per node lock, which is much slower even with no contention. There still can be lots of objects in a dead memcg cache (e.g. hundreds of megabytes of dcache), so such performance degradation is not acceptable, IMO. OTOH, we already have cache_reap running periodically for each cache. Making it drain all free objects in dead caches won't impact performance at all, neither will it complicate the code. The only downside is a dead cache won't be destroyed immediately after it becomes unused, but since cache_reap runs pretty often (each several secs), it shouldn't result in any problems, I guess. Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>