Re: mm: critical shortage of bounce buffers

[Alan Cox]

> > Its in the high mem handling routines. It means the machine stalled for
> > a moment doing I/O because it had no memory below 1Gb to use.
> 
> But why does it need to have memory below 1Gb ?? Normally, 32bit PCI DMA
> controllers (such as network cards and disk controllers) can access up to 4GB of
> physical memory within the machine, so unless you are using the CONFIG_HIGHMEM4G
> option it shouldn't need bounce buffers. Or am I missing something here
> (something like the second physical GB is actually in the address range
> 4GB->)???

The core code doesn't know if the device is PIO or DMA, and it cannot 
pass virtually unmapped objects to the block layer. This is what Jens has
been fixing.