Re: Block device throttling [Re: Distributed storage.]

[Evgeniy Polyakov]

On Sun, Aug 12, 2007 at 11:44:00PM -0700, Daniel Phillips (phillips@xxxxxxxxx) wrote:
> On Sunday 12 August 2007 22:36, I wrote:
> > Note!  There are two more issues I forgot to mention earlier.
> 
> Oops, and there is also:
> 
> 3) The bio throttle, which is supposed to prevent deadlock, can itself 
> deadlock.  Let me see if I can remember how it goes.
> 
>   * generic_make_request puts a bio in flight
>   * the bio gets past the throttle and initiates network IO
>   * net calls sk_alloc->alloc_pages->shrink_caches
>   * shrink_caches submits a bio recursively to our block device
>   * this bio blocks on the throttle
>   * net may never get the memory it needs, and we are wedged

If system is in such condition, it is already broken - throttle limit
must be lowered (next time) not to allow such situation.

-- 
	Evgeniy Polyakov
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