On Mon, 2011-09-26 at 11:35 +0300, Gilad Ben-Yossef wrote: > Yes, the alloc in the flush_all path definitively needs to go. I > wonder if just to resolve that allocating the mask per cpu and not in > kmem_cache itself is not better - after all, all we need is a single > mask per cpu when we wish to do a flush_all and no per cache. The > memory overhead of that is slightly better. This doesn't cover the > cahce bounce issue. > > My thoughts regarding that were that since the flush_all() was a > rather rare operation it is preferable to do some more > work/interference here, if it allows us to avoid having to do more > work in the hotter alloc/dealloc paths, especially since it allows us > to have less IPIs that I figured are more intrusive then cacheline > steals (are they?) > > After all, for each CPU that actually needs to do a flush, we are > making the flush a bit more expensive because of the cache bounce just > before we send the IPI, but that IPI and further operations are an > expensive operations anyway. For CPUs that don't need to do a flush, I > replaced an IPI for a cacheline(s) steal. I figured it was still a > good bargain Hard to tell really, I've never really worked with these massive machines, biggest I've got is 2 nodes and for that I think your for_each_online_cpu() loop might indeed still be a win when compared to extra accounting on the alloc/free paths. The problem with a per-cpu cpumask is that you need to disable preemption over the whole for_each_online_cpu() scan and that's not really sane on very large machines as that can easily take a very long time indeed. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href