> On Sun, Aug 01, 2010 at 04:32:01PM +0800, KOSAKI Motohiro wrote: > > > On Wed, Jul 28, 2010 at 05:59:55PM +0800, KOSAKI Motohiro wrote: > > > > > On Wed, Jul 28, 2010 at 06:43:41PM +0900, KOSAKI Motohiro wrote: > > > > > > > On Wed, Jul 28, 2010 at 04:46:54PM +0800, Wu Fengguang wrote: > > > > > > > > The wait_on_page_writeback() call inside pageout() is virtually dead code. > > > > > > > > > > > > > > > > shrink_inactive_list() > > > > > > > > shrink_page_list(PAGEOUT_IO_ASYNC) > > > > > > > > pageout(PAGEOUT_IO_ASYNC) > > > > > > > > shrink_page_list(PAGEOUT_IO_SYNC) > > > > > > > > pageout(PAGEOUT_IO_SYNC) > > > > > > > > > > > > > > > > Because shrink_page_list/pageout(PAGEOUT_IO_SYNC) is always called after > > > > > > > > a preceding shrink_page_list/pageout(PAGEOUT_IO_ASYNC), the first > > > > > > > > pageout(ASYNC) converts dirty pages into writeback pages, the second > > > > > > > > shrink_page_list(SYNC) waits on the clean of writeback pages before > > > > > > > > calling pageout(SYNC). The second shrink_page_list(SYNC) can hardly run > > > > > > > > into dirty pages for pageout(SYNC) unless in some race conditions. > > > > > > > > > > > > > > > > > > > > > > It's possible for the second call to run into dirty pages as there is a > > > > > > > congestion_wait() call between the first shrink_page_list() call and the > > > > > > > second. That's a big window. > > > > > > > > > > > > > > > And the wait page-by-page behavior of pageout(SYNC) will lead to very > > > > > > > > long stall time if running into some range of dirty pages. > > > > > > > > > > > > > > True, but this is also lumpy reclaim which is depending on a contiguous > > > > > > > range of pages. It's better for it to wait on the selected range of pages > > > > > > > which is known to contain at least one old page than excessively scan and > > > > > > > reclaim newer pages. > > > > > > > > > > > > Today, I was successful to reproduce the Andres's issue. and I disagree this > > > > > > opinion. > > > > > > > > > > Is Andres's issue not covered by the patch "vmscan: raise the bar to > > > > > PAGEOUT_IO_SYNC stalls" because wait_on_page_writeback() was the > > > > > main problem? > > > > > > > > Well, "vmscan: raise the bar to PAGEOUT_IO_SYNC stalls" is completely bandaid and > > > > > > No joking. The (DEF_PRIORITY-2) is obviously too permissive and shall be fixed. > > > > > > > much IO under slow USB flash memory device still cause such problem even if the patch is applied. > > > > > > As for this patch, raising the bar to PAGEOUT_IO_SYNC reduces both > > > calls to congestion_wait() and wait_on_page_writeback(). So it > > > absolutely helps by itself. > > > > > > > But removing wait_on_page_writeback() doesn't solve the issue perfectly because current > > > > lumpy reclaim have multiple sick. again, I'm writing explaining mail..... > > > > > > Let's submit the two known working fixes first? > > > > Definitely, I can't oppose obvious test result (by another your mail) :-) > > > > OK, should go! > > Great. Shall I go first? My changelog has more background :) Sure. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
