Hi Fengguang:
Thanks for looking at this.
On Mon, Aug 15, 2011 at 6:48 AM, Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> Curt,
>
> Some thoughts about the interface..before dipping into the code.
>
> On Sat, Aug 13, 2011 at 06:47:25AM +0800, Curt Wohlgemuth wrote:
>> Add a new file, /proc/writeback/stats, which displays
>
> That's creating a new top directory in /proc. Do you have plans for
> adding more files under it?
Good question. We have several files under /proc/writeback in our
kernels that we created at various times, some of which are probably
no longer useful, but others seem to be. For example:
- congestion: prints # of calls, # of jiffies slept in
congestion_wait() / io_schedule_timeout() from various call points
- threshold_dirty : prints the current global FG threshold
- threshold_bg : prints the current global BG threshold
- pages_cleaned : prints the # pages sent to writeback -- same as
'nr_written' in /proc/vmstat (ours was earlier :-( )
- pages_dirtied (same as nr_dirtied in /proc/vmstat)
- prop_vm_XXX : print shift/events from vm_completions and vm_dirties
I'm not sure right now if global FG/BG thresholds appear anywhere in a
3.1 kernel; if so, the two threshold files above are superfluous. So
are the pages_cleaned/dirtied. The prop_vm files have not proven
useful to me. I think the congestion file has a lot of value,
especially in an IO-less throttling world...
>
>> machine global data for how many pages were cleaned for
>> which reasons. It also displays some additional counts for
>> various writeback events.
>>
>> These data are also available for each BDI, in
>> /sys/block/<device>/bdi/writeback_stats .
>
>> Sample output:
>>
>> page: balance_dirty_pages 2561544
>> page: background_writeout 5153
>> page: try_to_free_pages 0
>> page: sync 0
>> page: kupdate 102723
>> page: fdatawrite 1228779
>> page: laptop_periodic 0
>> page: free_more_memory 0
>> page: fs_free_space 0
>> periodic writeback 377
>> single inode wait 0
>> writeback_wb wait 1
>
> That's already useful data, and could be further extended (in
> future patches) to answer questions like "what's the writeback
> efficiency in terms of effective chunk size?"
>
> So in future there could be lines like
>
> pages: balance_dirty_pages 2561544
> chunks: balance_dirty_pages XXXXXXX
> works: balance_dirty_pages XXXXXXX
>
> or even derived lines like
>
> pages_per_chunk: balance_dirty_pages XXXXXXX
> pages_per_work: balance_dirty_pages XXXXXXX
>
> Another question is, how can the display format be script friendly?
> The current form looks not easily parse-able at least for "cut"..
I suppose you mean because of the variable number of tokens. Yeah,
this can be hard. Of course, I always just use "awk '{print $NF}'"
and it works for me :-) . But I'd be happy to change these to use a
consistent # of args.
Thanks,
Curt
> Thanks,
> Fengguang
>
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