Re: [Mesa3d-dev] dynamic code generation with gcc

[Gareth H. <ga...@va...>]

Keith Whitwell wrote:
> 
> But of course, we should never be getting rid of or aquiring new dma buffers;
> we should be just aging regions within a buffer we always hold, and perhaps in
> rare cases growing/shrinking it.
> 
> However, mprotect doesn't help you here either, as the regions being aged are
> pretty dynamic.

If only I could sit down and finish my dynamic heap code... :-)

My plan is to basically have a pool of 2-4 MB DMA regions, with each one
assigned to at most one context.  The context handles all allocation
within the buffer, and the regions are aged by the kernel when they are
flushed.  The flush is the only thing that you need to go into the
kernel for, and I can't really see any way around that.

(Note: current status is working allocation code in a single region,
need to finish off multiple regions, switching regions between contexts
and the like.  The new SAREA code will allow a finer grain of control
over the region, as we're currently limited to a 4K control page).

If you were lucky enough to fill your region, your next
LOCK_DMA_REGION() would automagically grab you another one.  I think
that's easier than trying to resize the current one.  Grabbing another
region may result in allocating and binding more AGP memory, but that's
a nice and transparent side effect.

-- Gareth