Re: oops with dual xeon 2.8ghz 4gb ram +smp, software raid, lvm, and xfs

From: Neil Brown (neilb_at_cse.unsw.edu.au)
Date: 11/25/04

  • Next message: Jeff Dike: "[PATCH] UML - Redo the signal delivery mechanism" 
    To: Andrew Morton <akpm@osdl.org>
Date:	Thu, 25 Nov 2004 11:14:39 +1100

    On Wednesday November 24, akpm@osdl.org wrote:
    > Neil Brown <neilb@cse.unsw.edu.au> wrote:
    > >
    > > Would the following (untested-but-seems-to-compile -
    > > explanation-of-concept) patch be at all reasonable to avoid stack
    > > depth problems with stacked block devices, or is adding stuff to
    > > task_struct frowned upon?
    >
    > It's always a tradeoff - we've put things in task_struct before to get
    > around sticky situations. Certainly, removing potentially unbounded stack
    > utilisation is a worthwhile thing to do.
    >
    > The patch bends my brain a bit.

    Recursion is like that (... like recursion, that is :-).

    > Shouldn't the queueing happen in
    > submit_bio()?

    Both md and dm call generic_make_request rather than submit_bio to
    start IO on slaves, so it wouldn't work in submit_bio. If dm and md
    were changes to use submit_bio, then the counts (page-in, page-out)
    would be quite different...

    >
    > Is bi_next free in there? If anyone tries to do synchronous I/O things
    > will get stuck.

    It is my understanding the bi_next is free. It is available for use
    by ->make_request_fn and below. __make_request uses it for chaining
    bio's together into a request. raid5 uses it for other things.

    If a ->make_request_fn did synchronous IO things would definitely get
    unstuck. But I don't think they should and doubt if they do (md
    certainly doesn't).

    NeilBrown
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