Re: [PATCH 3/3] writeback: tracking subsystems causing writeback
From: Michael Rubin
Date: Sat Jun 19 2010 - 13:50:32 EST
Thanks for looking at this.
On Sat, Jun 19, 2010 at 1:17 AM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
> Michael Rubin <mrubin@xxxxxxxxxx> writes:
>> # cat /sys/block/sda/bdi/writeback_stats
>> balance dirty pages 0
>> balance dirty pages waiting 0
>> periodic writeback 92024
>> periodic writeback exited 0
>> laptop periodic 0
>> laptop or bg threshold 0
>> free more memory 0
>> try to free pages 271
>> syc_sync 6
>> sync filesystem 0
>
> That exports a lot of kernel internals in /sys, presumably read by some
> applications. What happens with the applications if the kernel internals
> ever change? Will the application break?
>
> It would be bad to not be able to change the kernel because of
> such an interface.
I agree. This would put the kernel in a box a bit. Some of them
(sys_sync, periodic writeback, free_more_memory) I feel are generic
enough concepts that with some rewording of the labels they could be
exposed with no issue. "Balance_dirty_pages" is an example where that
won't work.
Are there alternatives to this? Maybe tracepoints that are compiled to be on?
A CONFIG_WRITEBACK_DEBUG that would expose this file?
Having this set of info readily available and collected makes
debugging a lot easier. But I admit I am not sure the best way to
expose them.
mrubin
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