On 05/01/18 12:01 PM, Keith Busch wrote:
On Fri, Jan 05, 2018 at 11:19:28AM -0700, Logan Gunthorpe wrote:
Although it is not explicitly stated anywhere, pci_alloc_p2pmem() should
always be at least 4k aligned. This is because the gen_pool that implements
it is created with PAGE_SHIFT for its min_alloc_order.
Ah, I see that now. Thanks for the explanation.
Does it need to be created with page sized minimum alloc order? That
granularity makes it difficult to fit SQs in CMB on archs with larger
pages when we only needed 4k alignment.
I was also hoping to extend this for PRP/SGL in CMB where even 4k is
too high a granularity to make it really useful.
It looks like creating the gen pool with a smaller minimum and
gen_pool_first_fit_order_align algo would satisfy my use cases, but I'm
not sure if there's another reason you've set it to page alignment.
I don't see any reason why we couldn't change this at some point if it
makes sense to. PAGE_SIZE just seemed like a suitable choice but I don't
think anything depends on it. In the end, I guess it depends on how
limited typical CMB buffers end up being.
Logan
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