IB/mlx4: Use 4K pages for kernel QP's WQE buffer

IB/mlx4: Use 4K pages for kernel QP's WQE buffer

In the current implementation, the driver tries to allocate contiguous
memory, and if it fails, it falls back to 4K fragmented allocation.

Once the memory is fragmented, the first allocation might take a lot
of time, and even fail, which can cause connection failures.

This patch changes the logic to always allocate with 4K granularity,
since it's more robust and more likely to succeed.

This patch was tested with Lustre and no performance degradation
was observed.

Note: This commit eliminates the "shrinking WQE" feature. This feature
depended on using vmap to create a virtually contiguous send WQ.
vmap use was abandoned due to problems with several processors (see the
commit cited below). As a result, shrinking WQE was available only with
physically contiguous send WQs. Allocating such send WQs caused the
problems described above.
Therefore, as a side effect of eliminating the use of large physically
contiguous send WQs, the shrinking WQE feature became unavailable.

Warning example:
worker/20:1: page allocation failure: order:8, mode:0x80d0
CPU: 20 PID: 513 Comm: kworker/20:1 Tainted: G OE ------------
Workqueue: ib_cm cm_work_handler [ib_cm]
Call Trace:
[<ffffffff81686d81>] dump_stack+0x19/0x1b
[<ffffffff81186160>] warn_alloc_failed+0x110/0x180
[<ffffffff8118a954>] __alloc_pages_nodemask+0x9b4/0xba0
[<ffffffff811ce868>] alloc_pages_current+0x98/0x110
[<ffffffff81184fae>] __get_free_pages+0xe/0x50
[<ffffffff8133f6fe>] swiotlb_alloc_coherent+0x5e/0x150
[<ffffffff81062551>] x86_swiotlb_alloc_coherent+0x41/0x50
[<ffffffffa056b4c4>] mlx4_buf_direct_alloc.isra.7+0xc4/0x180 [mlx4_core]
[<ffffffffa056b73b>] mlx4_buf_alloc+0x1bb/0x260 [mlx4_core]
[<ffffffffa0b15496>] create_qp_common+0x536/0x1000 [mlx4_ib]
[<ffffffff811c6ef7>] ? dma_pool_free+0xa7/0xd0
[<ffffffffa0b163c1>] mlx4_ib_create_qp+0x3b1/0xdc0 [mlx4_ib]
[<ffffffffa0b01bc2>] ? mlx4_ib_create_cq+0x2d2/0x430 [mlx4_ib]
[<ffffffffa0b21f20>] mlx4_ib_create_qp_wrp+0x10/0x20 [mlx4_ib]
[<ffffffffa08f152a>] ib_create_qp+0x7a/0x2f0 [ib_core]
[<ffffffffa06205d4>] rdma_create_qp+0x34/0xb0 [rdma_cm]
[<ffffffffa08275c9>] kiblnd_create_conn+0xbf9/0x1950 [ko2iblnd]
[<ffffffffa074077a>] ? cfs_percpt_unlock+0x1a/0xb0 [libcfs]
[<ffffffffa0835519>] kiblnd_passive_connect+0xa99/0x18c0 [ko2iblnd]

Fixes: 73898db04301 ("net/mlx4: Avoid wrong virtual mappings")
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>