[LSF/MM/BPF TOPIC] CMA reservation optimizations

[Juan Yescas <jyescas@google.com>]

Hi LSF organizers,

I would like to continue discussing this topic with the mm community:

"CMA reservation optimizations"

Note: There is already an email in the linux-mm mailing list that is
discussing this issue. The title is:

"CMA reservations require 32MiB alignment in 16KiB page size kernels
instead of 8MiB in 4KiB page size kernel"

Background

When the drivers reserve CMA memory in 16KiB kernels, the minimum
alignment is 32 MiB as per CMA_MIN_ALIGNMENT_BYTES. However, in 4KiB
kernels, the CMA alignment is 4MiB.

This is forcing the drivers to reserve more memory than required in
16KiB kernels,
even if they only require 4MiB or 8MiB.

reserved-memory {
      #address-cells = <2>;
      #size-cells = <2>;
      ranges;
      tpu_cma_reserve: tpu_cma_reserve {
            compatible = "shared-dma-pool";
            reusable;
           size = <0x0 0x2000000>; /* 32 MiB */
}

Thanks
Juan