On Thu, 2013-12-19 at 17:02 -0800, Andrew Morton wrote: > On Wed, 18 Dec 2013 15:53:59 +0900 Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote: > > > If parallel fault occur, we can fail to allocate a hugepage, > > because many threads dequeue a hugepage to handle a fault of same address. > > This makes reserved pool shortage just for a little while and this cause > > faulting thread who can get hugepages to get a SIGBUS signal. > > > > To solve this problem, we already have a nice solution, that is, > > a hugetlb_instantiation_mutex. This blocks other threads to dive into > > a fault handler. This solve the problem clearly, but it introduce > > performance degradation, because it serialize all fault handling. > > > > Now, I try to remove a hugetlb_instantiation_mutex to get rid of > > performance degradation. > > So the whole point of the patch is to improve performance, but the > changelog doesn't include any performance measurements! > > Please, run some quantitative tests and include a nice summary of the > results in the changelog. I was actually spending this afternoon testing these patches with Oracle (I haven't seen any issues so far) and unless Joonsoo already did so, I want to run these by the libhugetlb test cases - I got side tracked by futexes though :/ Please do consider that performance wise I haven't seen much in particular. The thing is, I started dealing with this mutex once I noticed it as the #1 hot lock in Oracle DB starts, but then once the faults are done, it really goes away. So I wouldn't say that the mutex is a bottleneck except for the first few minutes. > > This is terribly important, because if the performance benefit is > infinitesimally small or negative, the patch goes into the bit bucket ;) Well, this mutex is infinitesimally ugly and needs to die (as long as performance isn't hurt). Thanks, Davidlohr -- 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>