On Mon, Jan 17, 2011 at 05:32:22PM +0100, Johannes Weiner wrote: > On Mon, Jan 17, 2011 at 10:02:47AM -0500, Chris Mason wrote: > > Excerpts from Chris Mason's message of 2011-01-17 09:07:40 -0500: > > > > [ various crashes under load with current git ] > > > > > > > > I did have CONFIG_COMPACTION off for my latest reproduce. The last two > > > have been corruption on the page->lru lists, maybe that'll help narrow > > > our bisect pool down. > > > > I've reverted 744ed1442757767ffede5008bb13e0805085902e, and > > d8505dee1a87b8d41b9c4ee1325cd72258226fbc and the run has lasted longer > > than any runs in the past. > > > > I'll give this a few hours but they seem the most related to my various > > crashes so far. > > I went through the new batched activation code. Shaohua, can you > explain to me why the following sequence is not possible? > > 1. CPU A and B schedule activation of a page (PG_lru && !PG_active) > 2. CPU A flushes the page to the active list (PG_lru && PG_active) > 3. CPU A isolates the page for scanning/migration and > puts it on private list (!PG_lru && PG_active) > 4. CPU B flushes the page to the active list (!PG_lru && PG_active), > the deferred activation code now assumes putback mode and adds the page > to the active list, thus corrupting the link to the private list of CPU A > 5. CPU A does list_del() from the private list (like unmap_and_move() does) > and trips up on the corruption > In addition, PageLRU is a bad test in __activate_page for deciding whether the page needs to be unlinked. When a page is on a pagevec, it's not an LRU page and it's not on a linked list. When a page is on a private linked list, it's not an LRU page but it has to be removed from the private list before adding to the LRU to avoid list corruption. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>