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

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Date:	Tue, 26 May 2009 04:59:05 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, chris.mason@...cle.com,
	david@...morbit.com, hch@...radead.org, 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 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.

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