On Thu, 2019-08-01 at 17:07 +0100, Robin Murphy wrote:

On 2019-08-01 4:44 pm, Nicolas Saenz Julienne wrote:

quoted

On Wed, 2019-07-31 at 18:07 +0100, Catalin Marinas wrote:

quoted

On Wed, Jul 31, 2019 at 05:47:48PM +0200, Nicolas Saenz Julienne wrote:

quoted

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 1c4ffabbe1cb..f5279ef85756 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c

@@ -50,6 +50,13 @@
  s64 memstart_addr __ro_after_init = -1;
  EXPORT_SYMBOL(memstart_addr);
  
+/*
+ * We might create both a ZONE_DMA and ZONE_DMA32. ZONE_DMA is needed

if
there
+ * are periferals unable to address the first naturally aligned 4GB of
ram.
+ * ZONE_DMA32 will be expanded to cover the rest of that memory. If
such
+ * limitations doesn't exist only ZONE_DMA32 is created.
+ */

Shouldn't we instead only create ZONE_DMA to cover the whole 32-bit
range and leave ZONE_DMA32 empty? Can__GFP_DMA allocations fall back
onto ZONE_DMA32?

Hi Catalin, thanks for the review.

You're right, the GFP_DMA page allocation will fail with a nasty dmesg error
if
ZONE_DMA is configured but empty. Unsurprisingly the opposite situation is
fine
(GFP_DMA32 with an empty ZONE_DMA32).

Was that tested on something other than RPi4 with more than 4GB of RAM? 
(i.e. with a non-empty ZONE_NORMAL either way)

No, all I did is play around with RPi4's memory size (1 GB vs 4 GB).

I'll see If I can get access to a dts based board with more than 4 GB, If not
I'll try to fake it. It's not ideal but I can set the limit on 3 GB and have
the 3 areas created (with and witouth an empty ZONE_DMA32).

On top of that, now that you ask, I realise I neglected all the ACPI based
servers. I have access to some so I'll make sure I test everything on them too
for the next series.

Regards,
Nicolas