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. 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. mrubin -- 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
