linux-kernel - Re: [PATCH for-next v8 4/6] RDMA/rxe: Allow registering MRs for On-Demand Paging

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Message-ID: <20241209193358.GE2368570@nvidia.com>
Date: Mon, 9 Dec 2024 15:33:58 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Daisuke Matsuda <matsuda-daisuke@...itsu.com>
Cc: linux-rdma@...r.kernel.org, leon@...nel.org, zyjzyj2000@...il.com,
	linux-kernel@...r.kernel.org, rpearsonhpe@...il.com,
	lizhijian@...itsu.com
Subject: Re: [PATCH for-next v8 4/6] RDMA/rxe: Allow registering MRs for
 On-Demand Paging

On Wed, Oct 09, 2024 at 10:59:01AM +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 upper = rxe_mr_iova_to_index(mr, end - 1);
> +	unsigned long lower = rxe_mr_iova_to_index(mr, start);
> +	void *page, *entry;
> +
> +	XA_STATE(xas, &mr->page_list, lower);
> +
> +	xas_lock(&xas);
> +	while (xas.xa_index <= upper) {
> +		if (pfn_list[xas.xa_index] & HMM_PFN_WRITE) {
> +			page = xa_tag_pointer(hmm_pfn_to_page(pfn_list[xas.xa_index]),
> +					      RXE_ODP_WRITABLE_BIT);
> +		} else
> +			page = hmm_pfn_to_page(pfn_list[xas.xa_index]);

Like here:

> +	rxe_mr_set_xarray(mr, user_va, user_va + bcnt, umem_odp->pfn_list);

So this is just copying the pfn_list to the xarray? Why not just
directly use pfn_list instead?

Though, you'd have to lock it with the mutex, is that the issue?

Jason