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Date: Tue, 17 Mar 2026 15:28:55 +0100
From: Christoph Hellwig <hch@lst.de>
To: Chuck Lever <cel@kernel.org>
Cc: Leon Romanovsky <leon@kernel.org>, Christoph Hellwig <hch@lst.de>,
	NeilBrown <neilb@ownmail.net>, Jeff Layton <jlayton@kernel.org>,
	Olga Kornievskaia <okorniev@redhat.com>,
	Dai Ngo <dai.ngo@oracle.com>, Tom Talpey <tom@talpey.com>,
	linux-nfs@vger.kernel.org, linux-rdma@vger.kernel.org,
	Chuck Lever <chuck.lever@oracle.com>,
	Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH v3 4/4] svcrdma: Use contiguous pages for RDMA Read
 sink buffers
Message-ID: <20260317142855.GD4367@lst.de>
References: <20260313194201.5818-1-cel@kernel.org> <20260313194201.5818-5-cel@kernel.org>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Fri, Mar 13, 2026 at 03:42:01PM -0400, Chuck Lever wrote:
> Suggested-by: Christoph Hellwig <hch@infradead.org>

I think that's a bit too much credit.  I just wondered why sunrpc can't
coalesce pages itself.

> +#if PAGE_SIZE < SZ_64K
> +
> +/*
> + * Limit contiguous RDMA Read sink allocations to 64KB
> + * (order-4 on 4KB-page systems). Higher orders risk
> + * allocation failure under __GFP_NORETRY, which would
> + * negate the benefit of the contiguous fast path.
> + */
> +#define SVC_RDMA_CONTIG_MAX_ORDER	get_order(SZ_64K)

Isn't the limit really an order and thus grows with the page size,
instead of based on a fixed size?

> +	o = get_order(nr_pages << PAGE_SHIFT);
> +	if (o > SVC_RDMA_CONTIG_MAX_ORDER)
> +		o = SVC_RDMA_CONTIG_MAX_ORDER;

Use min()?