[PATCH 1/1] [RFC] drm/ttm: Don't init dma32_zone on 64-bit systems

[Thomas Hellstrom]

Hmm,

This zone was intended to stop TTM page allocations from exhausting the 
DMA32 zone. IIRC dma_alloc_coherent() uses DMA32 by default, which means 
if we drop this check, other devices may stop functioning unexpectedly?

However, in the end I'd expect the kernel page allocation system to make 
sure there are some pages left in the DMA32 zone, otherwise random 
non-IO page allocations would also potentially exhaust the DMA32 zone 
without anybody caring, which means removing this zone wouldn't be any 
worse than whatever other subsystems may be doing already...

/Thomas


On 2/16/19 12:02 AM, Kuehling, Felix wrote:
> This is an RFC. I'm not sure this is the right solution, but it
> highlights the problem I'm trying to solve.
>
> The dma32_zone limits the acc_size of all allocated BOs to 2GB. On a
> 64-bit system with hundreds of GB of system memory and GPU memory,
> this can become a bottle neck. We're seeing TTM memory allocation
> failures not because we're truly out of memory, but because we're
> out of space in the dma32_zone for the acc_size needed for our BO
> book-keeping.
>
> Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
> CC: thellstrom at vmware.com
> CC: christian.koenig at amd.com
> ---
>   drivers/gpu/drm/ttm/ttm_memory.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_memory.c b/drivers/gpu/drm/ttm/ttm_memory.c
> index f1567c3..bb05365 100644
> --- a/drivers/gpu/drm/ttm/ttm_memory.c
> +++ b/drivers/gpu/drm/ttm/ttm_memory.c
> @@ -363,7 +363,7 @@ static int ttm_mem_init_highmem_zone(struct ttm_mem_global *glob,
>   	glob->zones[glob->num_zones++] = zone;
>   	return 0;
>   }
> -#else
> +#elifndef CONFIG_64BIT
>   static int ttm_mem_init_dma32_zone(struct ttm_mem_global *glob,
>   				   const struct sysinfo *si)
>   {
> @@ -441,7 +441,7 @@ int ttm_mem_global_init(struct ttm_mem_global *glob)
>   	ret = ttm_mem_init_highmem_zone(glob, &si);
>   	if (unlikely(ret != 0))
>   		goto out_no_zone;
> -#else
> +#elifndef CONFIG_64BIT
>   	ret = ttm_mem_init_dma32_zone(glob, &si);
>   	if (unlikely(ret != 0))
>   		goto out_no_zone;