On Fri, Jan 4, 2013 at 10:16 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > I still have quite a few instances of 2-6 ms of latency due to > "call_rwsem_down_read_failed __do_page_fault do_page_fault > page_fault". Any idea why? I don't know any great way to figure out > who is holding mmap_sem at the time. Given what my code is doing, I > suspect the contention is due to mmap or munmap on a file. MCL_FUTURE > is set, and MAP_POPULATE is not set. > > It could be the other thread calling mmap and getting preempted (or > otherwise calling schedule()). Grr. The simplest way to find out who's holding the lock too long might be to enable CONFIG_LOCK_STATS. This will slow things down a little, but give you lots of useful information including which threads hold mmap_sem the longest and the call stack for where they grab it from. See Documentation/lockstat.txt I think munmap is a likely culprit, as it still happens with mmap_sem held for write (I do plan to go work on this next). But it's hard to be sure without lockstats :) -- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies. -- 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>