From 2f800fbd777b792de54187088df19a7df0251254 Mon Sep 17 00:00:00 2001 From: Wu Fengguang Date: Mon, 8 Aug 2011 15:22:00 -0600 Subject: [PATCH] writeback: fix dirtied pages accounting on redirty De-account the accumulative dirty counters on page redirty. Page redirties (very common in ext4) will introduce mismatch between counters (a) and (b) a) NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied b) NR_WRITTEN, BDI_WRITTEN This will introduce systematic errors in balanced_rate and result in dirty page position errors (ie. the dirty pages are no longer balanced around the global/bdi setpoints). Acked-by: Jan Kara Acked-by: Peter Zijlstra Signed-off-by: Wu Fengguang --- include/linux/writeback.h | 2 ++ mm/page-writeback.c | 19 +++++++++++++++++++ 2 files changed, 21 insertions(+) diff --git a/include/linux/writeback.h b/include/linux/writeback.h index 05eaf5e3aad7..b30419cd425e 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -197,6 +197,8 @@ void writeback_set_ratelimit(void); void tag_pages_for_writeback(struct address_space *mapping, pgoff_t start, pgoff_t end); +void account_page_redirty(struct page *page); + /* pdflush.c */ extern int nr_pdflush_threads; /* Global so it can be exported to sysctl read-only. */ diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 5d1ef5d8613a..96b3e7aa705c 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1824,6 +1824,24 @@ int __set_page_dirty_nobuffers(struct page *page) } EXPORT_SYMBOL(__set_page_dirty_nobuffers); +/* + * Call this whenever redirtying a page, to de-account the dirty counters + * (NR_DIRTIED, BDI_DIRTIED, tsk->nr_dirtied), so that they match the written + * counters (NR_WRITTEN, BDI_WRITTEN) in long term. The mismatches will lead to + * systematic errors in balanced_dirty_ratelimit and the dirty pages position + * control. + */ +void account_page_redirty(struct page *page) +{ + struct address_space *mapping = page->mapping; + if (mapping && mapping_cap_account_dirty(mapping)) { + current->nr_dirtied--; + dec_zone_page_state(page, NR_DIRTIED); + dec_bdi_stat(mapping->backing_dev_info, BDI_DIRTIED); + } +} +EXPORT_SYMBOL(account_page_redirty); + /* * When a writepage implementation decides that it doesn't want to write this * page for some reason, it should redirty the locked page via @@ -1832,6 +1850,7 @@ EXPORT_SYMBOL(__set_page_dirty_nobuffers); int redirty_page_for_writepage(struct writeback_control *wbc, struct page *page) { wbc->pages_skipped++; + account_page_redirty(page); return __set_page_dirty_nobuffers(page); } EXPORT_SYMBOL(redirty_page_for_writepage);