From fe3cba17c49471e99d3421e675fc8b3deaaf0b70 Mon Sep 17 00:00:00 2001 From: Fengguang Wu Date: Thu, 19 Jul 2007 01:48:07 -0700 Subject: mm: share PG_readahead and PG_reclaim Share the same page flag bit for PG_readahead and PG_reclaim. One is used only on file reads, another is only for emergency writes. One is used mostly for fresh/young pages, another is for old pages. Combinations of possible interactions are: a) clear PG_reclaim => implicit clear of PG_readahead it will delay an asynchronous readahead into a synchronous one it actually does _good_ for readahead: the pages will be reclaimed soon, it's readahead thrashing! in this case, synchronous readahead makes more sense. b) clear PG_readahead => implicit clear of PG_reclaim one(and only one) page will not be reclaimed in time it can be avoided by checking PageWriteback(page) in readahead first c) set PG_reclaim => implicit set of PG_readahead will confuse readahead and make it restart the size rampup process it's a trivial problem, and can mostly be avoided by checking PageWriteback(page) first in readahead d) set PG_readahead => implicit set of PG_reclaim PG_readahead will never be set on already cached pages. PG_reclaim will always be cleared on dirtying a page. so not a problem. In summary, a) we get better behavior b,d) possible interactions can be avoided c) racy condition exists that might affect readahead, but the chance is _really_ low, and the hurt on readahead is trivial. Compound pages also use PG_reclaim, but for now they do not interact with reclaim/readahead code. Signed-off-by: Fengguang Wu Cc: Rusty Russell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page-writeback.c | 1 + 1 file changed, 1 insertion(+) (limited to 'mm/page-writeback.c') diff --git a/mm/page-writeback.c b/mm/page-writeback.c index e62482718012..51b3eb6ab445 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -920,6 +920,7 @@ int clear_page_dirty_for_io(struct page *page) BUG_ON(!PageLocked(page)); + ClearPageReclaim(page); if (mapping && mapping_cap_account_dirty(mapping)) { /* * Yes, Virginia, this is indeed insane. -- cgit v1.2.3