[PATCH] vmscan: remove wait_on_page_writeback() from pageout()
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From: Wu Fengguang on 28 Jul 2010 04:50 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. 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. So it's bad idea anyway to call wait_on_page_writeback() inside pageout(). CC: Andy Whitcroft <apw(a)shadowen.org> Signed-off-by: Wu Fengguang <fengguang.wu(a)intel.com> --- mm/vmscan.c | 13 ++----------- 1 file changed, 2 insertions(+), 11 deletions(-) --- linux-next.orig/mm/vmscan.c 2010-07-28 16:22:21.000000000 +0800 +++ linux-next/mm/vmscan.c 2010-07-28 16:23:35.000000000 +0800 @@ -324,8 +324,7 @@ typedef enum { * pageout is called by shrink_page_list() for each dirty page. * Calls ->writepage(). */ -static pageout_t pageout(struct page *page, struct address_space *mapping, - enum pageout_io sync_writeback) +static pageout_t pageout(struct page *page, struct address_space *mapping) { /* * If the page is dirty, only perform writeback if that write @@ -384,14 +383,6 @@ static pageout_t pageout(struct page *pa return PAGE_ACTIVATE; } - /* - * Wait on writeback if requested to. This happens when - * direct reclaiming a large contiguous area and the - * first attempt to free a range of pages fails. - */ - if (PageWriteback(page) && sync_writeback == PAGEOUT_IO_SYNC) - wait_on_page_writeback(page); - if (!PageWriteback(page)) { /* synchronous write or broken a_ops? */ ClearPageReclaim(page); @@ -727,7 +718,7 @@ static unsigned long shrink_page_list(st goto keep_locked; /* Page is dirty, try to write it out here */ - switch (pageout(page, mapping, sync_writeback)) { + switch (pageout(page, mapping)) { case PAGE_KEEP: goto keep_locked; case PAGE_ACTIVATE: -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |