ACK: [SRU][F][aws][PATCH 0/1] aws: disable CONFIG_DMA_CMA

[Colin Ian King]

On 20/05/2020 15:04, Andrea Righi wrote:
> BugLink: https://bugs.launchpad.net/bugs/1879711
> 
> [Impact]
> 
> The option CONFIG_DMA_CMA seems to cause hibernation failures on the
> t2.* instance types (Xen).
> 
> With this option enabled device drivers are allowed to use the
> Contiguous Memory Allocator (CMA) for DMA operations. So, drivers can
> allocate large physically-contiguous blocks of memory, instead of
> relying on the I/O map or scatter-gather support.
> 
> However, on resume, the memory used by DMA needs to be re-initialized /
> re-allocated, but it may fail to allocate large chunks of contiguous
> memory due to the fact that we also need to restore the hibernation
> image, using more memory and causing a system hang during the resume
> process.
> 
> [Test case]
> 
> Hibernate / resume any t2.* instance (especially t2.nano, where the
> problem seems to happen 100% of the times after 2 consecutive
> hibernate/resume cycles).
> 
> [Fix]
> 
> Disable CONFIG_DMA_CMA.
> 
> NOTE: this option is already disabled in the generic kernel (see LP:
> #1362261).
> 
> With this option disabled the success rate of hibernation on the t2.*
> instance types during our tests jumped to 100%.
> 
> [Regression potential]
> 
> It is a .config change, no regression potential except for the fact that
> disabling this option also disables the module 'etnaviv' (Vivante
> graphic card), that is not really needed in the aws kernel.
> 
> ----------------------------------------------------------------
> Andrea Righi (1):
>       UBUNTU: [Config] aws: disable CONFIG_DMA_CMA
> 
>  debian.aws/abi/5.4.0-1010.10/amd64/aws.modules |  1 -
>  debian.aws/abi/5.4.0-1010.10/arm64/aws.modules |  1 -
>  debian.aws/config/config.common.ubuntu         | 11 ++---------
>  3 files changed, 2 insertions(+), 11 deletions(-)
> 
> 
Makes sense to me.

Acked-by: Colin Ian King <colin.king at canonical.com>