Re: [patch for playing] 2.5.65 patch to support > 256 disks

[Nick Piggin <piggin@cyberone.com.au>]

Jens Axboe wrote:

>On Tue, Mar 25 2003, Nick Piggin wrote:
>
>>
>>Nice Jens. Very good in theory but I haven't looked at the
>>code too much yet.
>>
>>Would it be possible to have all queues allocate out of
>>the one global pool of free requests. This way you could
>>have a big minimum (say 128) and a big maximum
>>(say min(Mbytes, spindles).
>>
>
>Well not really, as far as I can see we _need_ a pool per queue. Imagine
>a bio handed to raid, needs to be split to 6 different queues. But our
>minimum is 4, deadlock possibility. It could probably be made to work,
>however I greatly prefer a per-queue reserve.
>
OK yeah you are right there. In light of your comment below
I'm happy with that. I was mostly worried about queues being
restricted to a small maximum.

>
>
>>This way memory usage is decoupled from the number of
>>queues, and busy spindles could make use of more
>>available free requests.
>>
>>Oh and the max value can easily be runtime tunable, right?
>>
>
>Sure. However, they don't really mean _anything_. Max is just some
>random number to prevent one queue going nuts, and could be completely
>removed if the vm works perfectly. Beyond some limit there's little
>benefit to doing that, though. But MAX could be runtime tunable. Min is
>basically just to make sure we don't kill ourselves, I don't see any
>point in making that runtime tunable. It's not really a tunable.
>
OK thats good then. I would like to see max removed, however perhaps
the VM isn't up to that yet. I'll be testing this when your code
solidifies!