Hi Mel, On Thu, Jul 22, 2010 at 05:42:09PM +0800, Mel Gorman wrote: > On Thu, Jul 22, 2010 at 04:52:10PM +0800, Wu Fengguang wrote: > > > Some insight on how the other writeback changes that are being floated > > > around might affect the number of dirty pages reclaim encounters would also > > > be helpful. > > > > Here is an interesting related problem about the wait_on_page_writeback() call > > inside shrink_page_list(): > > > > http://lkml.org/lkml/2010/4/4/86 I guess you've got the answers from the above thread, anyway here is the brief answers to your questions. > > > > The problem is, wait_on_page_writeback() is called too early in the > > direct reclaim path, which blocks many random/unrelated processes when > > some slow (USB stick) writeback is on the way. > > > > A simple dd can easily create a big range of dirty pages in the LRU > > list. Therefore priority can easily go below (DEF_PRIORITY - 2) in a > > typical desktop, which triggers the lumpy reclaim mode and hence > > wait_on_page_writeback(). > > > > Lumpy reclaim is for high-order allocations. A simple dd should not be > triggering it regularly unless there was a lot of forking going on at the > same time. dd could create the dirty file fast enough, so that no other processes are injecting pages into the LRU lists besides dd itself. So it's creating a large range of hard-to-reclaim LRU pages which will trigger this code + else if (sc->order && priority < DEF_PRIORITY - 2) + lumpy_reclaim = 1; > Also, how would a random or unrelated process get blocked on > writeback unless they were also doing high-order allocations? What was the > source of the high-order allocations? sc->order is 1 on fork(). Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>