Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 20 Jul 2023 09:06:12 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Nitesh Shetty <nj.shetty@samsung.com>
Cc:     Jens Axboe <axboe@kernel.dk>, Jonathan Corbet <corbet@lwn.net>,
        Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@kernel.org>, dm-devel@redhat.com,
        Keith Busch <kbusch@kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>,
        Chaitanya Kulkarni <kch@nvidia.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        martin.petersen@oracle.com, linux-scsi@vger.kernel.org,
        willy@infradead.org, hare@suse.de, djwong@kernel.org,
        bvanassche@acm.org, ming.lei@redhat.com, dlemoal@kernel.org,
        nitheshshetty@gmail.com, gost.dev@samsung.com,
        Kanchan Joshi <joshi.k@samsung.com>,
        Anuj Gupta <anuj20.g@samsung.com>, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v13 1/9] block: Introduce queue limits for copy-offload
 support
Message-ID: <20230720070612.GA4722@lst.de>
References: <20230627183629.26571-1-nj.shetty@samsung.com> <CGME20230627184000epcas5p1c7cb01eb1c70bc5a19f76ce21f2ec3f8@epcas5p1.samsung.com> <20230627183629.26571-2-nj.shetty@samsung.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230627183629.26571-2-nj.shetty@samsung.com>
User-Agent: Mutt/1.5.17 (2007-11-01)
Precedence: bulk

Just a little heads up:  I think we need to properly solve the
hw vs user limit as the various ad-hoc mechanisms tend to be
broken and don't scale.  I plan to start looking into that the
next days.

On Wed, Jun 28, 2023 at 12:06:15AM +0530, Nitesh Shetty wrote:
> Add device limits as sysfs entries,
>         - copy_offload (RW)
>         - copy_max_bytes (RW)
>         - copy_max_bytes_hw (RO)
> 
> Above limits help to split the copy payload in block layer.
> copy_offload: used for setting copy offload(1) or emulation(0).
> copy_max_bytes: maximum total length of copy in single payload.
> copy_max_bytes_hw: Reflects the device supported maximum limit.

Why do we need the separate copy_offload boolean vs just looking
at the max_bytes value?