linux-kernel - Re: [PATCH v20 02/12] Add infrastructure for copy offload in block and request layer.

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Date: Tue, 4 Jun 2024 04:44:34 -0700
From: Bart Van Assche <bvanassche@....org>
To: Christoph Hellwig <hch@....de>
Cc: Nitesh Shetty <nj.shetty@...sung.com>, Damien Le Moal
 <dlemoal@...nel.org>, Jens Axboe <axboe@...nel.dk>,
 Jonathan Corbet <corbet@....net>, Alasdair Kergon <agk@...hat.com>,
 Mike Snitzer <snitzer@...nel.org>, Mikulas Patocka <mpatocka@...hat.com>,
 Keith Busch <kbusch@...nel.org>, Sagi Grimberg <sagi@...mberg.me>,
 Chaitanya Kulkarni <kch@...dia.com>, Alexander Viro
 <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>,
 Jan Kara <jack@...e.cz>, martin.petersen@...cle.com, david@...morbit.com,
 hare@...e.de, damien.lemoal@...nsource.wdc.com, anuj20.g@...sung.com,
 joshi.k@...sung.com, nitheshshetty@...il.com, gost.dev@...sung.com,
 linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, dm-devel@...ts.linux.dev,
 linux-nvme@...ts.infradead.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v20 02/12] Add infrastructure for copy offload in block
 and request layer.

On 6/3/24 21:40, Christoph Hellwig wrote:
> There is no requirement to process them synchronously, there is just
> a requirement to preserve the order.  Note that my suggestion a few
> arounds ago also included a copy id to match them up.  If we don't
> need that I'm happy to leave it away.  If need it it to make stacking
> drivers' lifes easier that suggestion still stands.

Including an ID in REQ_OP_COPY_DST and REQ_OP_COPY_SRC operations sounds
much better to me than abusing the merge infrastructure for combining
these two operations into a single request. With the ID-based approach
stacking drivers are allowed to process copy bios asynchronously and it
is no longer necessary to activate merging for copy operations if
merging is disabled (QUEUE_FLAG_NOMERGES).

Thanks,

Bart.