path: root/mm
diff options
authorMichael Rubin <mrubin@google.com>2010-10-26 14:21:33 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-10-26 16:52:06 -0700
commitf629d1c9bd0dbc44a6c4f9a4a67d1646c42bfc6f (patch)
tree22ac36b494b40e17bfa68e85a094b9cc4b2f6093 /mm
parent0def08e3acc2c9c934e4671487029aed52202d42 (diff)
mm: add account_page_writeback()
To help developers and applications gain visibility into writeback behaviour this patch adds two counters to /proc/vmstat. # grep nr_dirtied /proc/vmstat nr_dirtied 3747 # grep nr_written /proc/vmstat nr_written 3618 These entries allow user apps to understand writeback behaviour over time and learn how it is impacting their performance. Currently there is no way to inspect dirty and writeback speed over time. It's not possible for nr_dirty/nr_writeback. These entries are necessary to give visibility into writeback behaviour. We have /proc/diskstats which lets us understand the io in the block layer. We have blktrace for more in depth understanding. We have e2fsprogs and debugsfs to give insight into the file systems behaviour, but we don't offer our users the ability understand what writeback is doing. There is no way to know how active it is over the whole system, if it's falling behind or to quantify it's efforts. With these values exported users can easily see how much data applications are sending through writeback and also at what rates writeback is processing this data. Comparing the rates of change between the two allow developers to see when writeback is not able to keep up with incoming traffic and the rate of dirty memory being sent to the IO back end. This allows folks to understand their io workloads and track kernel issues. Non kernel engineers at Google often use these counters to solve puzzling performance problems. Patch #4 adds a pernode vmstat file with nr_dirtied and nr_written Patch #5 add writeback thresholds to /proc/vmstat Currently these values are in debugfs. But they should be promoted to /proc since they are useful for developers who are writing databases and file servers and are not debugging the kernel. The output is as below: # grep threshold /proc/vmstat nr_pages_dirty_threshold 409111 nr_pages_dirty_background_threshold 818223 This patch: This allows code outside of the mm core to safely manipulate page writeback state and not worry about the other accounting. Not using these routines means that some code will lose track of the accounting and we get bugs. Modify nilfs2 to use interface. Signed-off-by: Michael Rubin <mrubin@google.com> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Reviewed-by: Wu Fengguang <fengguang.wu@intel.com> Cc: KONISHI Ryusuke <konishi.ryusuke@lab.ntt.co.jp> Cc: Jiro SEKIBA <jir@unicus.jp> Cc: Dave Chinner <david@fromorbit.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
1 files changed, 12 insertions, 1 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index e3bccac1f02..94159819a65 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1129,6 +1129,17 @@ void account_page_dirtied(struct page *page, struct address_space *mapping)
+ * Helper function for set_page_writeback family.
+ * NOTE: Unlike account_page_dirtied this does not rely on being atomic
+ * wrt interrupts.
+ */
+void account_page_writeback(struct page *page)
+ inc_zone_page_state(page, NR_WRITEBACK);
* For address_spaces which do not use buffers. Just tag the page as dirty in
* its radix tree.
@@ -1366,7 +1377,7 @@ int test_set_page_writeback(struct page *page)
ret = TestSetPageWriteback(page);
if (!ret)
- inc_zone_page_state(page, NR_WRITEBACK);
+ account_page_writeback(page);
return ret;