On Sun, Jun 21, 2020 at 01:43:02PM -0700, David Rientjes wrote:
> When a DMA coherent pool is depleted, allocation failures may or may not
> get reported in the kernel log depending on the allocator.
>
> The admin does have a workaround, however, by using coherent_pool= on the
> kernel command line.
>
> Provide some guidance on the failure and a recommended minimum size for
> the pools (double the size).
>
> Signed-off-by: David Rientjes <rient...@google.com>
Tested-by: Guenter Roeck <li...@roeck-us.net>
Also confirmed that coherent_pool=256k works around the crash
I had observed.
Guenter
> ---
> kernel/dma/pool.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> --- a/kernel/dma/pool.c
> +++ b/kernel/dma/pool.c
> @@ -239,12 +239,16 @@ void *dma_alloc_from_pool(struct device *dev, size_t
> size,
> }
>
> val = gen_pool_alloc(pool, size);
> - if (val) {
> + if (likely(val)) {
> phys_addr_t phys = gen_pool_virt_to_phys(pool, val);
>
> *ret_page = pfn_to_page(__phys_to_pfn(phys));
> ptr = (void *)val;
> memset(ptr, 0, size);
> + } else {
> + WARN_ONCE(1, "DMA coherent pool depleted, increase size "
> + "(recommended min coherent_pool=%zuK)\n",
> + gen_pool_size(pool) >> 9);
> }
> if (gen_pool_avail(pool) < atomic_pool_size)
> schedule_work(&atomic_pool_work);
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