On Tue, Jun 10, 2014 at 07:18:34PM +0400, Vladimir Davydov wrote: > On Tue, Jun 10, 2014 at 09:26:19AM -0500, Christoph Lameter wrote: > > On Tue, 10 Jun 2014, Vladimir Davydov wrote: > > > > > Frankly, I incline to shrinking dead SLAB caches periodically from > > > cache_reap too, because it looks neater and less intrusive to me. Also > > > it has zero performance impact, which is nice. > > > > > > However, Christoph proposed to disable per cpu arrays for dead caches, > > > similarly to SLUB, and I decided to give it a try, just to see the end > > > code we'd have with it. > > > > > > I'm still not quite sure which way we should choose though... > > > > Which one is cleaner? > > To shrink dead caches aggressively, we only need to modify cache_reap > (see https://lkml.org/lkml/2014/5/30/271). Hmm, reap_alien, which is called from cache_reap to shrink per node alien object arrays, only processes one node at a time. That means with the patch I gave a link to above it will take up to (REAPTIMEOUT_AC*nr_online_nodes) seconds to destroy a virtually empty dead cache, which may be quite long on large machines. Of course, we can make reap_alien walk over all alien caches of the current node, but that will probably hurt performance... > > To zap object arrays for dead caches (this is what this patch does), we > have to: > - set array_cache->limit to 0 for each per cpu, shared, and alien array > caches on kmem_cache_shrink; > - make cpu/node hotplug paths init new array cache sizes to 0; > - make free paths (__cache_free, cache_free_alien) handle zero array > cache size properly, because currently they doesn't. > > So IMO the first one (reaping dead caches periodically) requires less > modifications and therefore is cleaner. -- 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>