Patch #1 sets up some helper functions for account_page_dirty Patch #2 sets up some helper functions for account_page_writeback Patch #3 adds writeback visibility in /proc/vmstat 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_cleaned /proc/vmstat nr_cleaned 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 add writeback thresholds to /proc/vmstat # grep threshold /proc/vmstat nr_pages_dirty_threshold 409111 nr_pages_dirty_background_threshold 818223 The files that report the dirty thresholds belong in /proc/vmstat. They are meant for application writers so should not be in debugfs. But since they are more related to internals of writeback, albeit internals that are fundamental to how it works, /proc/sys/vm is not appropriate. These values are reported in debugfs already in /debug/bdi/default/stats. Since debugfs is intended for kernel developers and /proc for applications there is an argument to put it in /proc. Not sure if that's enough but thought it worth attaching. Michael Rubin (4): mm: exporting account_page_dirty mm: account_page_writeback added writeback: nr_dirtied and nr_cleaned in /proc/vmstat writeback: Reporting dirty thresholds in /proc/vmstat drivers/base/node.c | 14 ++++++++++++++ fs/ceph/addr.c | 8 +------- fs/nilfs2/segment.c | 2 +- include/linux/mm.h | 1 + include/linux/mmzone.h | 4 ++++ mm/page-writeback.c | 16 +++++++++++++++- mm/vmstat.c | 8 ++++++++ 7 files changed, 44 insertions(+), 9 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
