On 06/07/2016 05:59 AM, Shawn Guo wrote:
Hi,
I'm using a separate CMA region than the system default one for
a particular device to avoid fragmentation. It does help. But under
certain circumstance (memory shortage), it seems some of the pages in
the region will be used by system. The really bad thing is that when
a CMA allocation tries to move these occupied pages around, it just
fails to do so with messages like "alloc_contig_range: ... PFNs busy".
These pages thus become holes in a contiguous block and prevent the
allocation from succeeding.
Is it possible to make a CMA absolutely for a particular device, and
even system movable pages cannot use the memory? I can reserve a memory
region from kernel and manage it with some custom and private interface
for that particular device. But obviously, the standard dma-mapping API
and established underneath CMA infrastructural is more desirable to use,
right?
This is an arm64 device running on 4.1 kernel. Any comments or
suggestions will be appreciated. Thanks.
Shawn
You could try backporting the ZONE_CMA patches
http://article.gmane.org/gmane.linux.kernel.mm/152016 . The primary problem
there was CMA utilization but there was some discussion about migration
success as well http://article.gmane.org/gmane.linux.kernel/2228789
If that doesn't work for you, I think the 'reusable' property can be dropped
and it should just become a DMA coherent pool. I haven't tested this though.
Thanks,
Laura
