Re: [PATCH] [Request for inclusion] Filesystem in Userspace

Pavel Machek
2004-11-19T09:46:41Z

Hi!

> > The GFP_IO and GFP_FS pages are the _real_ protectors. They don't dip into
> > the (very limited) set of pages, they say "we can still free 90% of
> > memory, we just have to ignore that dangerous 10%".
>
> I don't see how this makes more problems to userspace filesystems.
> When you clear GFP_IO or GFP_FS for an allocation you are limiting
> yourself from freeing some sort of memory. But that will not make it
> easier to actually _get_ that memory.
>
> With FUSE the allocation is NOT limited. Deadlock will not happen
> since page writeback is non-blocking, so while more FUSE backed pages
> can't be written, other filesystem's pages can be written back. The
> situation is better not worse.
>
> What am I missing?

I believe problem is when there are no other filesystem's
pages.... and at that point FUSE is worse than kernel filesystems
because you do not have reserved pools to use for freeing memory.

Pavel
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