Messages in this thread | | | Date | Sat, 15 Jun 2002 11:14:05 +0200 | From | Jens Axboe <> | Subject | Re: bio_chain: proposed solution for bio_alloc failure and large IO simplification |
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On Sat, Jun 15 2002, Adam J. Richter wrote: > >> So, I need a fourth location at in generic_make_request > >> just before the call to q->make_request_fn, like so: > >> > >> if (q->make_request_fn != __make_request) { > >> int flags; > >> spin_lock_irqsave(q->lock, flags); > >> clear_hint(bio); > >> spin_unlock_irqrestore(q->lock, flags); > >> } > >> ret = q->make_request_fn(q, bio); > > >Irk, this is ugly. But how you are moving away from the initial goal (or > >maybe this was your goal the whole time, just a single merge hint?) of > >passing back the hint instead of maintaing it in the queue. So let me > >ask, are you aware of the last_merge I/O scheduler hint? Which does > >exactly this already... > > The code that I think I more or less have in my head has not > changed (aside from that fourth test). > > Although I was not aware of q->last_merge, I see that it is > not what I want. I want up to one hint per request, for the last bio > in the request. bi_hint would be null for all bio's except possibly > the last bio in a request. I do not want just one hint per queue.
.. which, as far as I can see, brings us right back into the problems with stalling the i/o and other nastiness. So far your approach seems hackish at best, but ->
> If it is unclear what I mean, perhaps I really need to code it > up to explain it. and we can discuss it from there.
go ahead and code it up if you want and we can discuss it some more.
-- Jens Axboe
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