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Date: Thu, 15 Jan 2026 17:29:29 +0100
From: Christoph Hellwig <hch@lst.de>
To: Chuck Lever <cel@kernel.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>, Leon Romanovsky <leon@kernel.org>,
	Christoph Hellwig <hch@lst.de>, linux-rdma@vger.kernel.org,
	linux-nfs@vger.kernel.org, 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>,
	Chuck Lever <chuck.lever@oracle.com>
Subject: Re: [PATCH v1 4/4] svcrdma: use bvec-based RDMA read/write API
Message-ID: <20260115162929.GC17257@lst.de>
References: <20260114143948.3946615-1-cel@kernel.org> <20260114143948.3946615-5-cel@kernel.org>
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On Wed, Jan 14, 2026 at 09:39:48AM -0500, Chuck Lever wrote:
> The structure size reduction is significant: the previous inline
> scatterlist array of RPCSVC_MAXPAGES entries (4KB or more) is
> replaced with a pointer to a dynamically allocated bvec array,
> bringing the fixed structure size down to approximately 100 bytes.

Can you explain why this switches to the dynamic allocation?
To me that seems like a separate trade-off to bvec vs scatterlist.

>   * Each WR chain handles a single contiguous server-side buffer,
> - * because scatterlist entries after the first have to start on
> + * because bio_vec entries after the first have to start on
>   * page alignment. xdr_buf iovecs cannot guarantee alignment.

For both the old and new version, can you explain they have to
start on a page boundary?  Because that's not how scatterlists or
bvecs work in general.  I guess this just documents the sunrpc
limits, but somehow projects it to these structures?