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    SubjectRe: Possible dcache BUG


    On Fri, 6 Aug 2004, Gene Heskett wrote:
    >
    > Linus, Andrew, should I apply this patch too at the next remake?

    Might be worth it, but it's more important to see any oops at all, or lack
    of oopses..

    > FWIW, I'm still up (20:38) this morning, and showing plenty (127+
    > megs) of free memory. No crash, no odd log (other than samba
    > squawking about some option thats been changed & I haven't fixed the
    > smb.conf) so far.
    >
    > I'm beginning to like this test patch, Linus, thanks :)

    If the only thing you have done is add the list_del_init() debugging
    patch, then the only thing that has changed is really the access patterns
    to uncached memory.

    The original list_del_init() tries to only do a few single _writes_ to the
    dentries around it. The added debugging will do _reads_ (and thus bring it
    into the cache) of the dentry pointers of the dentries around it.

    If that change makes a real difference, I really only see two
    possibilities:
    - there really is a prefetch bug (or possibly, there's a bug in our
    prefetch fixup code, and the known prefetch bug just triggers the
    problem indirectly)
    - it just changes the timing enough that whatever bug you hit went away.

    Now, Chris Shoemaker reported dentry problems on a intel CPU and said that
    wli had seen something too, but I'm wondering whether Chris and wli might
    have been seeing the knfsd/xfs-related dentry bug that I found yesterday.
    So I think the prefetch theory is still alive, but we should check with
    Chris. Chris?

    Linus
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