This is missing from 3.0.y and 3.2.y; should we have it?
Ben.
---
From: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Date: Mon, 8 Aug 2011 15:22:00 -0600
Subject: writeback: fix dirtied pages accounting on redirty
commit 2f800fbd777b792de54187088df19a7df0251254 upstream.
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 <jack@xxxxxxx>
Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
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 05eaf5e..b30419c 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 5d1ef5d..96b3e7a 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1825,6 +1825,24 @@ 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
* redirty_page_for_writepage() and it should then unlock the page and return 0
@@ -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);
--
Ben Hutchings
I'm not a reverse psychological virus. Please don't copy me into your sig.
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