2012/8/19, Fengguang Wu <fengguang.wu@xxxxxxxxx>: > On Sat, Aug 18, 2012 at 05:50:02AM -0400, Namjae Jeon wrote: >> From: Namjae Jeon <namjae.jeon@xxxxxxxxxxx> >> >> This patch is based on suggestion by Wu Fengguang: >> https://lkml.org/lkml/2011/8/19/19 >> >> kernel has mechanism to do writeback as per dirty_ratio and >> dirty_background >> ratio. It also maintains per task dirty rate limit to keep balance of >> dirty pages at any given instance by doing bdi bandwidth estimation. >> >> Kernel also has max_ratio/min_ratio tunables to specify percentage of >> writecache >> to control per bdi dirty limits and task throtelling. >> >> However, there might be a usecase where user wants a writeback tuning >> parameter to flush dirty data at desired/tuned time interval. >> >> dirty_background_time provides an interface where user can tune >> background >> writeback start time using /sys/block/sda/bdi/dirty_background_time >> >> dirty_background_time is used alongwith average bdi write bandwidth >> estimation >> to start background writeback. > > Here lies my major concern about dirty_background_time: the write > bandwidth estimation is an _estimation_ and will sure become wildly > wrong in some cases. So the dirty_background_time implementation based > on it will not always work to the user expectations. > > One important case is, some users (eg. Dave Chinner) explicitly take > advantage of the existing behavior to quickly create & delete a big > 1GB temp file without worrying about triggering unnecessary IOs. > Hi. Wu. Okay, I have a question. If making dirty_writeback_interval per bdi to tune short interval instead of background_time, We can get similar performance improvement. /sys/block/<device>/bdi/dirty_writeback_interval /sys/block/<device>/bdi/dirty_expire_interval NFS write performance improvement is just one usecase. If we can set interval/time per bdi, other usecases will be created by applying. How do you think ? >The numbers are impressive! FYI, I tried another NFS specific approach >to avoid big NFS COMMITs, which achieved similar performance gains: >nfs: writeback pages wait queue >https://lkml.org/lkml/2011/10/20/235 Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
