linux-kernel - Re: [PATCH for-next v5 5/7] RDMA/rxe: Allow registering MRs for On-Demand Paging

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Message-ID: <ZIdFXfDu4IMKE+BQ@nvidia.com>
Date:   Mon, 12 Jun 2023 13:18:37 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Daisuke Matsuda <matsuda-daisuke@...itsu.com>
Cc:     linux-rdma@...r.kernel.org, leonro@...dia.com,
        zyjzyj2000@...il.com, linux-kernel@...r.kernel.org,
        rpearsonhpe@...il.com, yangx.jy@...itsu.com, lizhijian@...itsu.com,
        y-goto@...itsu.com
Subject: Re: [PATCH for-next v5 5/7] RDMA/rxe: Allow registering MRs for
 On-Demand Paging

On Thu, May 18, 2023 at 05:21:50PM +0900, Daisuke Matsuda wrote:

> +static void rxe_mr_set_xarray(struct rxe_mr *mr, unsigned long start,
> +			      unsigned long end, unsigned long *pfn_list)
> +{
> +	unsigned long lower, upper, idx;
> +	struct page *page;
> +
> +	lower = rxe_mr_iova_to_index(mr, start);
> +	upper = rxe_mr_iova_to_index(mr, end);
> +
> +	/* make pages visible in xarray. no sleep while taking the lock */
> +	spin_lock(&mr->page_list.xa_lock);
> +	for (idx = lower; idx <= upper; idx++) {
> +		page = hmm_pfn_to_page(pfn_list[idx]);
> +		__xa_store(&mr->page_list, idx, page, GFP_ATOMIC);

All of these loops can be performance improved a lot by using xas
loops

>  				    unsigned long cur_seq)
> @@ -54,3 +72,105 @@ static bool rxe_ib_invalidate_range(struct mmu_interval_notifier *mni,
>  const struct mmu_interval_notifier_ops rxe_mn_ops = {
>  	.invalidate = rxe_ib_invalidate_range,
>  };
> +
> +#define RXE_PAGEFAULT_RDONLY BIT(1)
> +#define RXE_PAGEFAULT_SNAPSHOT BIT(2)
> +static int rxe_odp_do_pagefault(struct rxe_mr *mr, u64 user_va, int bcnt, u32 flags)
> +{
> +	int np;
> +	u64 access_mask;
> +	bool fault = !(flags & RXE_PAGEFAULT_SNAPSHOT);
> +	struct ib_umem_odp *umem_odp = to_ib_umem_odp(mr->umem);
> +
> +	access_mask = ODP_READ_ALLOWED_BIT;
> +	if (umem_odp->umem.writable && !(flags & RXE_PAGEFAULT_RDONLY))
> +		access_mask |= ODP_WRITE_ALLOWED_BIT;
> +
> +	/*
> +	 * ib_umem_odp_map_dma_and_lock() locks umem_mutex on success.
> +	 * Callers must release the lock later to let invalidation handler
> +	 * do its work again.
> +	 */
> +	np = ib_umem_odp_map_dma_and_lock(umem_odp, user_va, bcnt,
> +					  access_mask, fault);
> +	if (np < 0)
> +		return np;
> +
> +	/* umem_mutex is still locked here, so we can use hmm_pfn_to_page()
> +	 * safely to fetch pages in the range.

All the comments should be in the style like the first one, not the
second

> +	 */
> +	rxe_mr_set_xarray(mr, user_va, user_va + bcnt, umem_odp->pfn_list);
> +
> +	return np;
> +}
> +
> +static int rxe_odp_init_pages(struct rxe_mr *mr)
> +{
> +	int ret;
> +	struct ib_umem_odp *umem_odp = to_ib_umem_odp(mr->umem);
> +
> +	ret = rxe_odp_do_pagefault(mr, mr->umem->address, mr->umem->length,
> +				   RXE_PAGEFAULT_SNAPSHOT);

Probably suffix this with "and_lock"

> +	mr->odp_enabled = true;
> +	mr->umem = &umem_odp->umem;
> +	mr->access = access_flags;
> +	mr->ibmr.length = length;
> +	mr->ibmr.iova = iova;
> +	mr->page_offset = ib_umem_offset(&umem_odp->umem);
> +
> +	err = rxe_odp_init_pages(mr);
> +	if (err) {
> +		ib_umem_odp_release(umem_odp);
> +		return err;
> +	}
> +
> +	err = rxe_mr_fill_pages_from_sgt(mr, &umem_odp->umem.sgt_append.sgt);

Uh? What is this? The sgt is not used in the ODP mode?

> diff --git a/drivers/infiniband/sw/rxe/rxe_verbs.h b/drivers/infiniband/sw/rxe/rxe_verbs.h
> index b6fbd9b3d086..de5a982c7c7e 100644
> --- a/drivers/infiniband/sw/rxe/rxe_verbs.h
> +++ b/drivers/infiniband/sw/rxe/rxe_verbs.h
> @@ -333,6 +333,8 @@ struct rxe_mr {
>  	u32			nbuf;
>  
>  	struct xarray		page_list;
> +
> +	bool			odp_enabled;

You can tell from the umem, don't need a flag

Jason