linux-kernel - Re: [PATCH 04/12] writeback: switch to per-bdi threads for flushing data

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Message-ID: <20090526090741.GE11363@kernel.dk>
Date:	Tue, 26 May 2009 11:07:42 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, chris.mason@...cle.com,
	david@...morbit.com, akpm@...ux-foundation.org,
	yanmin_zhang@...ux.intel.com
Subject: Re: [PATCH 04/12] writeback: switch to per-bdi threads for
	flushing data

On Tue, May 26 2009, Christoph Hellwig wrote:
> On Tue, May 26, 2009 at 10:56:48AM +0200, Jens Axboe wrote:
> > >   Hmm, so each BDI flusher thread is going to sync all the superblocks?
> > > Isn't there a better way? I suppose we *should* be able to somehow go
> > > from a BDI to a superblock (or maybe a list of those) so that we can write
> > > per-fs metadata not bound to inodes.
> > 
> > I just moved the sync_supers() to the bdi_forker_task(). That makes it
> > global at the same interval of wakeups, instead of doing in the bdi
> > threads. It would be nice to sync locally instead, but that's something
> > that can wait for later (if ever).
> 
> For now it might be easier to just have a separate thread for calling
> sync_supers instead of interwinding it with the data writeback.
> 
> Btw, XFS currently has a per-device thread for that, to avoid any global
> contention.

That's basically what the mentioned change does. bdi_forker_task() is a
the default_backing_dev task, it does little more than simply setup new
threads and such.

-- 
Jens Axboe

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