>> 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. I looked at this patch a bit. The worth of this is to improve the cache hit ratio of heap. 1) For single thread applications, heap is frequently largest mapping in the process. 2) For java VM, "java -Xms1000m -Xmx1000m HelloWorld" makes following /proc/<pid>/smaps entry. That said, JVM allocate single heap even if applications are multi threaded. c1800000-100000000 rw-p 00000000 00:00 0 Size: 1024000 kB Rss: 244 kB Pss: 244 kB Shared_Clean: 0 kB Shared_Dirty: 0 kB Private_Clean: 0 kB Private_Dirty: 244 kB Referenced: 244 kB Anonymous: 244 kB AnonHugePages: 0 kB Swap: 0 kB KernelPageSize: 4 kB MMUPageSize: 4 kB That's good. However, we know there is a situation that this patch doesn't work. glibc makes per thread heap (arena) by default. So, it is not to be expected works well on glibc multi threaded programs. That's a slightly big limitation. Anyway, I haven't observed real performance difference because most big penalty of find_vma come from taking mmap_sem, not rb-tree search. Another and additional input are welcome. But I myself haven't convinced this patch works everywhere. -- 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>