Messages in this thread | | | Date | Tue, 12 Apr 2005 22:04:40 +1000 | From | Nick Piggin <> | Subject | Re: Processes stuck on D state on Dual Opteron |
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Nick Piggin wrote: > Nick Piggin wrote: > >> Chen, Kenneth W wrote: > > >>> I like the patch a lot and already did bench it on our db setup. >>> However, >>> I'm seeing a negative regression compare to a very very crappy patch >>> (see >>> attached, you can laugh at me for doing things like that :-). >>> >> >> OK - if we go that way, perhaps the following patch may be the >> way to do it. >> > > Here. >
Actually yes this is good I think.
What I was worried about is that you could lose some fairness due to not being put on the queue before allocation.
This is probably a silly thing to worry about, because up until that point things aren't really deterministic anyway (and before this patchset it would try doing a GFP_ATOMIC allocation first anyway).
However after the subsequent locking rework, both these get_request() calls will be performed under the same lock - giving you the same fairness. So it is nothing to worry about anyway!
It is a bit subtle: get_request may only drop the lock and return NULL (after retaking the lock), if we fail on a memory allocation. If we just fail due to unavailable queue slots, then the lock is never dropped. And the mem allocation can't fail because it is a mempool alloc with GFP_NOIO.
Nick
-- SUSE Labs, Novell Inc.
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