* Davidlohr Bueso <davidlohr@xxxxxx> wrote: > On Fri, 2013-11-01 at 16:38 -0400, KOSAKI Motohiro wrote: > > (11/1/13 4:17 PM), Davidlohr Bueso wrote: > > > > > While caching the last used vma already does a nice job avoiding > > > having to iterate the rbtree in find_vma, we can improve. After > > > studying the hit rate on a load of workloads and environments, it > > > was seen that it was around 45-50% - constant for a standard desktop > > > system (gnome3 + evolution + firefox + a few xterms), and multiple > > > java related workloads (including Hadoop/terasort), and aim7, which > > > indicates it's better than the 35% value documented in the code. > > > > > > By also caching the largest vma, that is, the one that contains most > > > addresses, there is a steady 10-15% hit rate gain, putting it above > > > the 60% region. This improvement comes at a very low overhead for a > > > miss. Furthermore, systems with !CONFIG_MMU keep the current logic. > > > > I'm slightly surprised this cache makes 15% hit. Which application get > > a benefit? You listed a lot of applications, but I'm not sure which is > > highly depending on largest vma. > > Well I chose the largest vma because it gives us a greater chance of > being already cached when we do the lookup for the faulted address. > > The 15% improvement was with Hadoop. According to my notes it was at > ~48% with the baseline kernel and increased to ~63% with this patch. > > In any case I didn't measure the rates on a per-task granularity, but at > a general system level. When a system is first booted I can see that the > mmap_cache access rate becomes the determinant factor and when adding a > workload it doesn't change much. One exception to this was a kernel > build, where we go from ~50% to ~89% hit rate on a vanilla kernel. ~90% during a kernel build is pretty impressive. Still the ad-hoc nature of the caching worries me a bit - but I don't have any better ideas myself. [I've Cc:-ed Linus, in case he has any better ideas.] Thanks, Ingo -- 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>