On Wed, 18 Apr 2012 16:28:31 +0100 Mel Gorman <mgorman@xxxxxxx> wrote: > > <SNIP> > > > > [PATCH] mm: fix s390 BUG by using __set_page_dirty_no_writeback on swap > > > > Mel reports a BUG_ON(slot == NULL) in radix_tree_tag_set() on s390 3.0.13: > > called from __set_page_dirty_nobuffers() when page_remove_rmap() tries to > > transfer dirty flag from s390 storage key to struct page and radix_tree. > > > > That would be because of reclaim's shrink_page_list() calling add_to_swap() > > on this page at the same time: first PageSwapCache is set (causing > > page_mapping(page) to appear as &swapper_space), then page->private set, > > then tree_lock taken, then page inserted into radix_tree - so there's > > an interval before taking the lock when the radix_tree slot is empty. > > > > Yes, makes sense. > > > We could fix this by moving __add_to_swap_cache()'s spin_lock_irq up > > before SetPageSwapCache, with error case ClearPageSwapCache moved up > > under tree_lock too. > > > > This can be done if/when swapper_space can make proper use of the dirty > tag information. > > > But a better fix is just to do what's five years overdue. Ken Chen > > added __set_page_dirty_no_writeback() (if !PageDirty TestSetPageDirty) > > for tmpfs to skip all that radix_tree overhead, and swap is just the same: > > it ignores the radix_tree tag, and does not participate in dirty page > > accounting, so should be using __set_page_dirty_no_writeback() too. > > > > Reported-by: Mel Gorman <mgorman@xxxxxxx> > > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> > > Acked-by: Mel Gorman <mgorman@xxxxxxx> > > I've sent a kernel based on this patch to the s390 folk that originally > reported the bug. Hopefully they'll test and get back to me in a few > days. > > Thanks Hugh. Indeed, thanks Hugh. The patches so far were not pretty at all.. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>