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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
- 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?

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