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DragonFly kernel List (threaded) for 2006-01
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Re: a take at cache coherency

From: "Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx>
Date: Fri, 27 Jan 2006 13:23:20 +0100

[forgot to post]

On 25.01.2006, at 14:41, Csaba Henk wrote:
I'd still use a ncp_shadowroot to get O(1) locking.
While you deref the the shadowroot pointer to go for the group lock,
the group might get broken up, and the shadowroot info will be stale.

This can't happen as we still have kernel locking. At the moment there won't be any two threads running in parallel accessing namecache records. Only if one of them blocks, another thread might sneak in. So doing a ->ncp_shadowinfo->ncp_exlocks++ is guarranteed to work (at the moment, when we make the namecache free of the BGL, we'll have to change the lock to something more sophisticated, but we're not there yet.)


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