On Wed, May 22, 2013 at 09:13:58AM +1000, Dave Chinner wrote: > On Mon, May 13, 2013 at 09:12:31AM +0100, Mel Gorman wrote: > > This series does not fix all the current known problems with reclaim but > > it addresses one important swapping bug when there is background IO. > > .... > > > > 3.10.0-rc1 3.10.0-rc1 > > vanilla lessdisrupt-v4 > > Page Ins 1234608 101892 > > Page Outs 12446272 11810468 > > Swap Ins 283406 0 > > Swap Outs 698469 27882 > > Direct pages scanned 0 136480 > > Kswapd pages scanned 6266537 5369364 > > Kswapd pages reclaimed 1088989 930832 > > Direct pages reclaimed 0 120901 > > Kswapd efficiency 17% 17% > > Kswapd velocity 5398.371 4635.115 > > Direct efficiency 100% 88% > > Direct velocity 0.000 117.817 > > Percentage direct scans 0% 2% > > Page writes by reclaim 1655843 4009929 > > Page writes file 957374 3982047 > > Lots more file pages are written by reclaim. Is this from kswapd > or direct reclaim? If it's direct reclaim, what happens when you run > on a filesystem that doesn't allow writeback from direct reclaim? > It's from kswapd. There is a check in shrink_page_list that prevents direct reclaim writing pages out for exactly the reason that some filesystems ignore it. > Also, what does this do to IO patterns and allocation? This tends > to indicate that the background flusher thread is not doing the > writeback work fast enough when memory is low - can you comment on > this at all, Mel? > There are two aspects to it. As processes are not longer being pushed to swap but kswapd is still reclaiming a similar number of pages, it is scanning through the file LRUs faster before flushers have a chance to flush pages. kswapd starts writing pages if the zone gets marked "reclaim dirty" which happens if enough dirty pages are encountered at the end of the LRU that are !PageWriteback. If this flag is set too early then more writes from kswapd context occur -- I'll look into it. On a related note, I've found with Jan Kara that the PageWriteback check does not work in all cases. Some filesystems will have buffer pages that are PageDirty with all clean buffers or with buffers locked for IO that are !PageWriteback which will also confuse when "reclaim dirty" gets set. The patches are still being a work in progress. -- Mel Gorman SUSE Labs -- 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>