On Thu, Apr 15, 2010 at 4:33 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > On Thu, Apr 15, 2010 at 10:27:09AM -0700, Suleiman Souhlal wrote: >> >> On Apr 15, 2010, at 2:32 AM, Dave Chinner wrote: >> >> >On Thu, Apr 15, 2010 at 01:05:57AM -0700, Suleiman Souhlal wrote: >> >> >> >>On Apr 14, 2010, at 9:11 PM, KOSAKI Motohiro wrote: >> >> >> >>>Now, vmscan pageout() is one of IO throuput degression source. >> >>>Some IO workload makes very much order-0 allocation and reclaim >> >>>and pageout's 4K IOs are making annoying lots seeks. >> >>> >> >>>At least, kswapd can avoid such pageout() because kswapd don't >> >>>need to consider OOM-Killer situation. that's no risk. >> >>> >> >>>Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> >> >> >> >>What's your opinion on trying to cluster the writes done by pageout, >> >>instead of not doing any paging out in kswapd? >> > >> >XFS already does this in ->writepage to try to minimise the impact >> >of the way pageout issues IO. It helps, but it is still not as good >> >as having all the writeback come from the flusher threads because >> >it's still pretty much random IO. >> >> Doesn't the randomness become irrelevant if you can cluster enough >> pages? > > No. If you are doing full disk seeks between random chunks, then you > still lose a large amount of throughput. e.g. if the seek time is > 10ms and your IO time is 10ms for each 4k page, then increasing the > size ito 64k makes it 10ms seek and 12ms for the IO. We might increase > throughput but we are still limited to 100 IOs per second. We've > gone from 400kB/s to 6MB/s, but that's still an order of magnitude > short of the 100MB/s full size IOs with little in way of seeks > between them will acheive on the same spindle... What I meant was that, theoretically speaking, you could increase the maximum amount of pages that get clustered so that you could get 100MB/s, although it most likely wouldn't be a good idea with the current patch. -- Suleiman -- 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>