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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> From: Damien Le Moal Organization: Western Digital Research In-Reply-To: <20221123205740.463185-9-bvanassche@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 11/24/22 05:57, Bart Van Assche wrote: > Add support for configuring the maximum segment size. > > Add support for segments smaller than the page size. > > This patch enables testing segments smaller than the page size with a > driver that does not call blk_rq_map_sg(). > > Cc: Christoph Hellwig > Cc: Ming Lei > Cc: Damien Le Moal > Cc: Chaitanya Kulkarni > Signed-off-by: Bart Van Assche > --- > drivers/block/null_blk/main.c | 20 +++++++++++++++++--- > drivers/block/null_blk/null_blk.h | 1 + > 2 files changed, 18 insertions(+), 3 deletions(-) > > diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c > index 1f154f92f4c2..bc811ab52c4a 100644 > --- a/drivers/block/null_blk/main.c > +++ b/drivers/block/null_blk/main.c > @@ -157,6 +157,10 @@ static int g_max_sectors; > module_param_named(max_sectors, g_max_sectors, int, 0444); > MODULE_PARM_DESC(max_sectors, "Maximum size of a command (in 512B sectors)"); > > +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 ? > +module_param_named(max_segment_size, g_max_segment_size, int, 0444); > +MODULE_PARM_DESC(max_segment_size, "Maximum size of a segment in bytes"); > + > static unsigned int nr_devices = 1; > module_param(nr_devices, uint, 0444); > MODULE_PARM_DESC(nr_devices, "Number of devices to register"); > @@ -409,6 +413,7 @@ NULLB_DEVICE_ATTR(home_node, uint, NULL); > NULLB_DEVICE_ATTR(queue_mode, uint, NULL); > NULLB_DEVICE_ATTR(blocksize, uint, NULL); > NULLB_DEVICE_ATTR(max_sectors, uint, NULL); > +NULLB_DEVICE_ATTR(max_segment_size, uint, NULL); > NULLB_DEVICE_ATTR(irqmode, uint, NULL); > NULLB_DEVICE_ATTR(hw_queue_depth, uint, NULL); > NULLB_DEVICE_ATTR(index, uint, NULL); > @@ -532,6 +537,7 @@ static struct configfs_attribute *nullb_device_attrs[] = { > &nullb_device_attr_queue_mode, > &nullb_device_attr_blocksize, > &nullb_device_attr_max_sectors, > + &nullb_device_attr_max_segment_size, > &nullb_device_attr_irqmode, > &nullb_device_attr_hw_queue_depth, > &nullb_device_attr_index, > @@ -610,7 +616,8 @@ static ssize_t memb_group_features_show(struct config_item *item, char *page) > return snprintf(page, PAGE_SIZE, > "badblocks,blocking,blocksize,cache_size," > "completion_nsec,discard,home_node,hw_queue_depth," > - "irqmode,max_sectors,mbps,memory_backed,no_sched," > + "irqmode,max_sectors,max_segment_size,mbps," > + "memory_backed,no_sched," > "poll_queues,power,queue_mode,shared_tag_bitmap,size," > "submit_queues,use_per_node_hctx,virt_boundary,zoned," > "zone_capacity,zone_max_active,zone_max_open," > @@ -673,6 +680,7 @@ static struct nullb_device *null_alloc_dev(void) > dev->queue_mode = g_queue_mode; > dev->blocksize = g_bs; > dev->max_sectors = g_max_sectors; > + dev->max_segment_size = g_max_segment_size; > dev->irqmode = g_irqmode; > dev->hw_queue_depth = g_hw_queue_depth; > dev->blocking = g_blocking; > @@ -1214,6 +1222,8 @@ static int null_transfer(struct nullb *nullb, struct page *page, > unsigned int valid_len = len; > int err = 0; > > + WARN_ONCE(len > dev->max_segment_size, "%u > %u\n", len, > + dev->max_segment_size); > if (!is_write) { > if (dev->zoned) > valid_len = null_zone_valid_read_len(nullb, > @@ -1249,7 +1259,8 @@ static int null_handle_rq(struct nullb_cmd *cmd) > > spin_lock_irq(&nullb->lock); > rq_for_each_segment(bvec, rq, iter) { > - len = bvec.bv_len; > + len = min(bvec.bv_len, nullb->dev->max_segment_size); > + bvec.bv_len = len; > err = null_transfer(nullb, bvec.bv_page, len, bvec.bv_offset, > op_is_write(req_op(rq)), sector, > rq->cmd_flags & REQ_FUA); > @@ -1276,7 +1287,8 @@ static int null_handle_bio(struct nullb_cmd *cmd) > > spin_lock_irq(&nullb->lock); > bio_for_each_segment(bvec, bio, iter) { > - len = bvec.bv_len; > + len = min(bvec.bv_len, nullb->dev->max_segment_size); > + bvec.bv_len = len; > err = null_transfer(nullb, bvec.bv_page, len, bvec.bv_offset, > op_is_write(bio_op(bio)), sector, > bio->bi_opf & REQ_FUA); > @@ -2088,6 +2100,7 @@ static int null_add_dev(struct nullb_device *dev) > nullb->q->queuedata = nullb; > blk_queue_flag_set(QUEUE_FLAG_NONROT, nullb->q); > blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, nullb->q); > + blk_queue_flag_set(QUEUE_FLAG_SUB_PAGE_SEGMENTS, nullb->q); > > mutex_lock(&lock); > rv = ida_simple_get(&nullb_indexes, 0, 0, GFP_KERNEL); > @@ -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". > > if (dev->virt_boundary) > blk_queue_virt_boundary(nullb->q, PAGE_SIZE - 1); > diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h > index 94ff68052b1e..6784ee9f5fda 100644 > --- a/drivers/block/null_blk/null_blk.h > +++ b/drivers/block/null_blk/null_blk.h > @@ -102,6 +102,7 @@ struct nullb_device { > unsigned int queue_mode; /* block interface */ > unsigned int blocksize; /* block size */ > unsigned int max_sectors; /* Max sectors per command */ > + unsigned int max_segment_size; /* Max size of a single DMA segment. */ > unsigned int irqmode; /* IRQ completion handler */ > unsigned int hw_queue_depth; /* queue depth */ > unsigned int index; /* index of the disk, only valid with a disk */ -- Damien Le Moal Western Digital Research