On 04/18/2018 10:55 AM, Michael S. Tsirkin wrote:
> Imagine you want to pass some data to card. > Natural thing is to just put it in a variable and start DMA. > However DMA API disallows stack access nowdays, > so it's natural to put this within struct device. > > See e.g. > > commit a725ee3e44e39dab1ec82cc745899a785d2a555e > Author: Andy Lutomirski <l...@kernel.org> > Date: Mon Jul 18 15:34:49 2016 -0700 > > virtio-net: Remove more stack DMA > Andy just moved the problem to another one, since at that time we already had vmalloc() fallback for at least 2 years. Note that my original patch had : p = kzalloc(alloc_size, GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT); if (!p) p = vzalloc(alloc_size); So really, normal (less than PAGE_SIZE) allocations would have almost-zero-chance to end up to vmalloc(one_page)