linux-kernel - Re: [PATCH 3/3] writeback: tracking subsystems causing writeback

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Date:	Sat, 19 Jun 2010 22:23:48 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Michael Rubin <mrubin@...gle.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, jack@...e.cz, akpm@...ux-foundation.org,
	david@...morbit.com, hch@....de, axboe@...nel.dk
Subject: Re: [PATCH 3/3] writeback: tracking subsystems causing writeback

Michael Rubin <mrubin@...gle.com> writes:
>
> 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.

Yes some rewording would be good.

> Are there alternatives to this? Maybe tracepoints that are compiled to be on?
> A CONFIG_WRITEBACK_DEBUG that would expose this file?

The classic way is to put it into debugfs which has a appropiate
disclaimer.

(although I fear we're weaning apps that depend on debugfs too
The growing ftrace user space code seems to all depend on debugfs)

> 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.

Maybe we just need a simpler writeback path that is not as complicated
to debug. 

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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