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SubjectRe: PF_MEMALLOC in 2.6
On Fri, Aug 20, 2004 at 10:52:51AM +0200, Oliver Neukum wrote:
> Am Freitag, 20. August 2004 10:06 schrieb Nick Piggin:
> > >>So I'd say try to find a way to only use PF_MEMALLOC on behalf of
> > >>a PF_MEMALLOC thread or use a mempool or something.
> > >
> > >
> > > Then the SCSI layer should pass down the flag.
> > >
> >
> > It would be ideal from the memory allocator's point of view to do it
> > on a per-request basis like that.
> >
> > When the rubber hits the road, I think it is probably going to be very
> > troublesome to do it right that way. For example, what happens when
> > your usb-thingy-thread blocks on a memory allocation while handling a
> > read request, then the system gets low on memory and someone tries to
> > free some by submitting a write request to the USB device?
>
> The write request will have to wait.

> Storage cannot do concurrent IO.

I'm going to jump in here and ask a simple question, what is the
blocking point that stops writes happening concurrent with reads?

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