Re: [RFC] fuse writable mmap design

[Miklos Szeredi <miklos@szeredi.hu>]

> > 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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