On 02/11/2016 11:51 PM, Andrew Morton wrote: > On Wed, 10 Feb 2016 16:24:16 -0800 Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> wrote: > >> On Wed, 2016-02-10 at 13:28 -0800, Andrew Morton wrote: >> >>> >>> If a process is unmapping 4MB then it's pretty crazy for us to be >>> hitting the percpu_counter 32 separate times for that single operation. >>> >>> Is there some way in which we can batch up the modifications within the >>> caller and update the counter less frequently? Perhaps even in a >>> single hit? >> >> I think the problem is the batch size is too small and we overflow >> the local counter into the global counter for 4M allocations. > > That's one way of looking at the issue. The other way (which I point > out above) is that we're calling vm_[un]_acct_memory too frequently > when mapping/unmapping 4M segments. > We call it only once per mmap() or munmap(), so there is nothing to improve. > Exactly which mmap.c callsite is causing this issue? > mmap_region() (or do_brk()) -> security_vm_enough_memory() -> __vm_enough_memory() -> vm_acct_memory() -- 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>