On Fri, Aug 20, 2010 at 04:16:09PM +0800, Michael Rubin wrote: > On Thu, Aug 19, 2010 at 7:51 PM, Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > > As Rik said, /proc/sys is not a suitable place. > > OK I'm convinced. > > > Frankly speaking I've worked on writeback for years and never felt > > the need to add these counters. What I often do is: > > > > $ vmmon -d 1 nr_writeback nr_dirty nr_unstable > > > > nr_writeback nr_dirty nr_unstable > > 68738 0 39568 > > 66051 0 42255 > > 63406 0 44900 > > 60643 0 47663 > > 57954 0 50352 > > 55264 0 53042 > > 52592 0 55715 > > 49922 0 58385 > > That is what I get when copying /dev/zero to NFS. > > > > I'm very interested in Google's use case for this patch, and why > > the simple /proc/vmstat based vmmon tool is not enough. > > So as I understand it from looking at the code vmmon is sampling > nr_writeback, nr_dirty which are exported versions of > global_page_state for NR_FILE_DIRTY and NR_WRITEBACK. These states are > a snapshot of the state of the kernel's pages. Namely how many dpages > ar ein writeback or dirty at the moment vmmon's acquire routine is > called. > > vmmon is sampling /proc/vstat and then displaying the difference from > the last time they sampled. If I am misunderstanding let me know. Maybe Andrew's vmmon does that. My vmmon always display the raw values :) It could be improved to do raw values for nr_dirty and differences for pgpgin by default. > This is good for the state of the system but as we compare > application, mm and io performance over long periods of time we are > interested in the surges and fluctuations of the rates of the > producing and consuming of dirty pages also. It can help isolate where > the problem is and also to compare performance between kernels and/or > applications. Yeah the accumulated dirty and writeback page counts could be useful. For example, for inspecting the dirty and writeback speed over time. That's not possible for nr_dirty/nr_writeback. Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>