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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.0 Subject: Re: [PATCH v2 8/8] null_blk: Support configuring the maximum segment size Content-Language: en-US To: Bart Van Assche , Jens Axboe Cc: linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, Christoph Hellwig , Adrian Hunter , Avri Altman , Ming Lei , Chaitanya Kulkarni References: <20221123205740.463185-1-bvanassche@acm.org> <20221123205740.463185-9-bvanassche@acm.org> <32feb681-e858-1a0c-b91d-3f0d85615a6d@opensource.wdc.com> <6c41f85b-7add-60d7-e131-71c3cfae80d0@acm.org> From: Damien Le Moal Organization: Western Digital Research In-Reply-To: <6c41f85b-7add-60d7-e131-71c3cfae80d0@acm.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On 12/1/22 07:29, Bart Van Assche wrote: > On 11/23/22 17:40, Damien Le Moal wrote: >> On 11/24/22 05:57, Bart Van Assche wrote: >>> +static unsigned int g_max_segment_size = 1UL << 31; >> >> 1UL is unsigned long be this var is unsigned int. Why not simply use >> UINT_MAX here ? You prefer the 2GB value ? If yes, then may be at least >> change that to "1U << 31", no ? >> >> [ ... ] >>> @@ -2106,6 +2119,7 @@ static int null_add_dev(struct nullb_device *dev) >>> dev->max_sectors = min_t(unsigned int, dev->max_sectors, >>> BLK_DEF_MAX_SECTORS); >>> blk_queue_max_hw_sectors(nullb->q, dev->max_sectors); >>> + blk_queue_max_segment_size(nullb->q, dev->max_segment_size); >> >> Should we keep the ability to use the kernel default value as the default >> here ? >> E.g. >> >> if (dev->max_segment_size) >> blk_queue_max_segment_size(nullb->q, >> dev->max_segment_size); >> >> If yes, then g_max_segment_size initial value should be 0, meaning "kernel >> default". > > Hi Damien, > > How about changing the default value for g_max_segment_size from > 1UL << 31 into BLK_MAX_SEGMENT_SIZE? That will simplify the code and > also prevents that this patch changes the behavior of the null_blk > driver if g_max_segment_size is not modified by the user. Sounds good to me. > > Thanks, > > Bart. > -- Damien Le Moal Western Digital Research