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

[Miklos Szeredi]

> The "allocation" is a fetch or store instruction by the FUSE process, 
> which generates a page fault.  To satisfy that, the kernel has to allocate 
> some real memory.  A fetch or store instruction doesn't fail when there's 
> no real memory available.  It just waits for the kernel to make some 
> available.  The kernel does that by picking some less deserving page and 
> evicting it.  That eviction may require a pageout.  If the guy who's doing 
> the fetch or store is the guy who's supposed to do that pageout, you have 
> a deadlock.

OK.  I still maintaintain, that this is an impossible situation, but
maybe I'm wrong. 

> Furthermore, it's not right for the write() to fail or for any process to 
> be killed by the OOM Killer.  The system has the resources to complete the 
> job.  It just hasn't scheduled them correctly and thus backed itself into 
> a corner.

Yes, but a kernel based filesystem would be in the same situation.
It's not a problem unique to userspace filesystems.  And I think the
kernel is careful enough not to get into the corner.  So there's no
problem.

Miklos
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