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).
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
include/linux/writeback.h | 2 ++
mm/page-writeback.c | 12 ++++++++++++
2 files changed, 14 insertions(+)
--- linux-next.orig/mm/page-writeback.c 2011-08-29 19:14:36.000000000 +0800
+++ linux-next/mm/page-writeback.c 2011-08-29 19:14:38.000000000 +0800
@@ -1836,6 +1836,17 @@ int __set_page_dirty_nobuffers(struct pa
}
EXPORT_SYMBOL(__set_page_dirty_nobuffers);
+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
@@ -1844,6 +1855,7 @@ 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);
--- linux-next.orig/include/linux/writeback.h 2011-08-29 19:14:32.000000000 +0800
+++ linux-next/include/linux/writeback.h 2011-08-29 19:14:38.000000000 +0800
@@ -175,6 +175,8 @@ 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. */
--
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