On Sun, May 29, 2011 at 02:17:02PM -0700, David Rientjes wrote:

On Sun, 29 May 2011, Dmitry Eremin-Solenikov wrote:

quoted

What about changing your patch for less intrusive one (to emit a
WARN_ON) for at least one
or two major releases and only then changing it back to the current state?

That would return memory that is not guaranteed to be within the first 
16MB of address space, so a GFP_DMA allocation would succeed with memory 
not from ZONE_DMA.

Err, no. GFP_DMA returns memory in a zone which the platform has setup.
There's nothing specific about it being "16MB" or any other size; the
arch can chose what size that is.

That's an invalid configuration, so users, including 
you, should at least edit their .config by hand to enable CONFIG_ZONE_DMA 
as a workaround.

Again, no.  This change has caused a load of previously working drivers
to suddenly start failing without _any_ explanation why or even warning
about the change.  It needs to start off as a WARN_ON() so that stuff
can be fixed, and then changed to a hard error.