[PATCH] nvme: use __GFP_NOWARN for iod allocation

[keith.busch@linux.intel.com (Keith Busch)]

On Thu, Jun 21, 2018@09:49:37AM -0600, Jens Axboe wrote:
> From: Jens Axboe <axboe at kernel.dk>
> Subject: [PATCH] nvme: limit max IO size and segments for pci-e
> 
> nvme requires an sg table allocation for each request. If the request
> is large, then the allocation can become quite large. For instance,
> with our default software settings of 1280KB IO size, we'll need
> 10248 bytes of sg table. That turns into a 2nd order allocation,
> which we can't always guarantee. If we fail the allocation, blk-mq
> will retry it later. But there's no guarantee that we'll EVER be
> able to allocate that much contigious memory.
> 
> Limit the IO size such that we never need more than a single page
> of memory. That's a lot faster and more reliable. Then back that
> allocation with a mempool, so that we know we'll always be able
> to succeed the allocation at some point.
> 
> Signed-off-by: Jens Axboe <axboe at kernel.dk>

This looks good to me. Thanks!

Acked-by: Keith Busch <keith.busch at intel.com>