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

From: Miklos Szeredi (miklos_at_szeredi.hu)
Date: 11/30/04

  • Next message: Roger Luethi: "Re: [PATCH] net/via-rhine: convert MODULE_PARM to module_param" 
    To: avi@argo.co.il
Date:	Tue, 30 Nov 2004 22:58:49 +0100

    > Looks like we are in a deadlock here :)
    >
    > However you choose to call it, it is unacceptable IMO.

    That I can agree with. I never said that this was a full solution,
    only that this shows, that the deadlock is not inherent in userspace
    filesystems.

    > So the userspace filesystem would pass that amount to the kernel. It's
    > not pretty, but it is workable.

    Not pretty is an understatement IMO.

    > >And this is not unique to userspace filesystems, as Rik van Riel
    > >pointed out earlier, network filesystems are also prone to deadlock:
    > >
    > >http://lkml.org/lkml/2004/11/27/81
    > >
    > >
    > >
    > This looks like a bug to me. Maybe jiggling the thresholds would help.

    Yes, and it's the jiggling I want to avoid.

    > The situation with userspace filesystems is:
    >
    > some process allocates memory, blocking on kswapd as memory is full
    > kswapd calls userspace filesystem to free memory
    > userspace filesystem calls kernel, which allocates memory and blocks
    > on kswapd
    > eventually all processes in the system block on kswapd
    >
    > I have observed (and fixed) this on a real system.

    I have observed it too (not yet fixed, but working on it). But
    realize that my proposal would excempt userspace filesystem pages from
    being blocked on by kswapd. That's a fundamental difference.

    Since you don't believe me, I'll have to make an implementation, so
    you can experiment with it. And if you'll still be able to cause a
    deadlock, I'll subject myself to extreme repentance, and promise never
    to touch an operating system ever again :)

    > with ramfs, once it accounts for memory, there would be no deadlock and
    > no oom.

    And once fuse acounts for memory there will be no deadlock and no oom.
    See the symmetry?

    Miklos
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  • Next message: Roger Luethi: "Re: [PATCH] net/via-rhine: convert MODULE_PARM to module_param"

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