RDMA/mlx5: Use SRCU properly in ODP prefetch
When working with SRCU protected xarrays the xarray itself should be the SRCU 'update' point. Instead prefetch is using live as the SRCU update point and this prevents switching the locking design to use the xarray instead. To solve this the prefetch must only read from the xarray once, and hold on to the actual MR pointer for the duration of the async operation. Incrementing num_pending_prefetch delays destruction of the MR, so it is suitable. Prefetch calls directly to the pagefault_mr using the MR pointer and only does a single xarray lookup. All the testing if a MR is prefetchable or not is now done only in the prefetch code and removed from the pagefault critical path. Link: https://lore.kernel.org/r/20191009160934.3143-2-jgg@ziepe.caReviewed-by:Artemy Kovalyov <artemyko@mellanox.com> Signed-off-by:
Jason Gunthorpe <jgg@mellanox.com>
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