linux-kernel - Re: [PATCH 03/17] writeback: introduce writeback_control.inodes

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Date:	Mon, 16 May 2011 06:40:16 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, Mel Gorman <mel@....ul.ie>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/17] writeback: introduce
 writeback_control.inodes_cleaned

On Mon, May 16, 2011 at 09:50:21AM +1000, Dave Chinner wrote:
> > - nr_to_write has always been "# of pages written" and writeback_sb_inodes()
> >   is actually making use of it to do page accounting in work->nr_pages.
> 
> Do we really care whether it's inodes or pages that are written? As
> far as i can tell it doesn't, because writing inodes generally
> requires more IO and so needs to be limited anyway.

We do care, but the current infrastructure already is bad enough to
not make it work.  E.g. when calling from balance_dirty_pages we
couldn't care less if the inode is written back, we just want pages
on stable storage, similar for wakeups from the VM code.  Sooner or
later there's no way around splitting page and inode writeback
completely.

> So put the accounting in the post-write code in
> writeback_single_inode() where we already check if the inode is
> still dirty or not.  Splitting per-inode post-write processing
> between writeback_single_inode and the higher level code is cludgy -
> I'd much prefer it done in only one place.

I'd tend to agree.  Especially as cleaner separation was the main
goal for getting rid of the writeback_control overload in the beginning.

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