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Thu, 30 Jul 2026 08:18:17 -0700 (PDT) Date: Thu, 30 Jul 2026 10:17:43 -0500 From: Ming Lei To: Caleb Sander Mateos Cc: Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 6/6] ublk: lift need_map check out of ublk_{,un}map_io() Message-ID: References: <20260729012951.3744582-1-csander@purestorage.com> <20260729012951.3744582-7-csander@purestorage.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260729012951.3744582-7-csander@purestorage.com> On Tue, Jul 28, 2026 at 07:29:51PM -0600, Caleb Sander Mateos wrote: > ublk_map_io() and ublk_unmap_io() are no-ops for ublk devices that > enable user copy or zero copy. However, the implementation is a bit > convoluted, returning the full request data length and relying on the > caller to check the return value against the request length. > UBLK_F_SHMEM_ZC recently added branches to skip the ublk_{,un}map_io() > call for I/Os using a shared-memory buffer. This is a more logical place > for the need_map check, so move it there from ublk_{,un}map_io(). > > Checking need_map early also avoids the expensive pointer-chasing for > the ublk_iod_is_shmem_zc() check in __ublk_complete_rq() in the common > case of a ublk device using user copy or zero copy. > > Signed-off-by: Caleb Sander Mateos Reviewed-by: Ming Lei Thanks, Ming