linux-kernel - Re: [RFC] fuse writable mmap design

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Message-Id: <E1Isl3p-0000rl-00@dorka.pomaz.szeredi.hu>
Date:	Thu, 15 Nov 2007 21:11:37 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	a.p.zijlstra@...llo.nl
CC:	miklos@...redi.hu, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [RFC] fuse writable mmap design

> > OTOH, I'm thinking about adding a per-fs limit (adjustable for
> > privileged mounts) of dirty+writeback.
> > 
> > I'm not sure how hard would it be to add support for this into
> > balance_dirty_pages().  So I'm thinking of a parameter in struct
> > backing_dev_info that is used to clip the calculated per-bdi threshold
> > below this maximum.
> > 
> > How would that affect the proportions algorithm?  What would happen to
> > the unused portion?  Would it adapt to the slowed writeback and
> > allocate it to some other writer?
> 
> The unused part is gone, I've not yet found a way to re-distribute this
> fairly.
> 
> [ It's one of my open-problems, I can do a min_ratio per bdi, but not
>   yet a max_ratio ]

OK, I'll bear this in mind.

Limiting the number of dirty+writeback to << dirty_thresh could still
make sense, since it could prevent a nasty filesystem from pinning
lots of kernel memory (which it can do without fuse in other ways, so
this is not very important IMO).

Miklos
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