From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8D16931717B for ; Tue, 24 Mar 2026 20:10:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774383045; cv=none; b=XB6V2INLYHcdeI16Iw7lD6Tn/dAcCWX2udonWh2edMY968jil1v7MirR0LhCb4nYyOSdpixF7yVX+LOJ69Fcy5G7XnjaI+tbzJ3TePa1cVays4q27odK8lR/6aKxMsjF24NnQfcLs7Im0T83mAKfrS3XYb3FDxQUzWKnPlBIil8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774383045; c=relaxed/simple; bh=JHOdDhFljM1k1sSBmX7I3426qAR4wbcnLHzu7CPur0o=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Mhx6yE7upya6Yuis/Pfet2eq+B2M+FODO/HVjGIPAjlkOf8rHa7k7wHRhLBvQAg8SVyCzaC6lWUqqSFs/RZ83V2r66+WpIUV6+eb3S1Mi0daAp7LtW8L8M6vILX7snIuXu3FAYrM4sFLkK1vRO3PKpisxRiaU7Sh+5h3z7siS/U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rcXGLGLW; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="rcXGLGLW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C0F6AC19424; Tue, 24 Mar 2026 20:10:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774383045; bh=JHOdDhFljM1k1sSBmX7I3426qAR4wbcnLHzu7CPur0o=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=rcXGLGLWxfCR2P3tnjW1IsvwaHkQA8OmS/I/I3BfhVfIp+PRa9js7D6J/ubgF+9sf 0JBRleEO2Vz+TZdqJJcehVyzqBmER3QWSQmqWYxJs/iEMaarIUr/Xp3k9favQ2fkWS GiemVpoIaTSlkFAkpxrXjVW+xhglGGQLeNvgUwu+K+sKoB7ojAtRKgP7N6rdporl8E s1vghnee1AGjy3AGuPyKcbG+T6//RWJANGeuZSx85G9sTb2bBi9eerg0sWh/Q8X9fW JqCaLB7pJX0WsQg0NmbB3SW8NRqe58zXNDGtCytA0ho12zGYpDBqoy6hbVMzORKYHj 6zVSJDdVO3uYA== Message-ID: <5cadb7e4-fce7-4a26-aa85-d968fb368e58@kernel.org> Date: Tue, 24 Mar 2026 13:10:38 -0700 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] null_blk: Support configuring the maximum segment size To: Bart Van Assche , Jens Axboe Cc: linux-block@vger.kernel.org, Christoph Hellwig , Ming Lei , Damien Le Moal , Chaitanya Kulkarni , Keith Busch , Johannes Thumshirn , Hans Holmberg , Christophe JAILLET , Nilay Shroff , Kees Cook , Hannes Reinecke , "Martin K. Petersen" References: <20260323202904.1248169-1-bvanassche@acm.org> <20260323202904.1248169-3-bvanassche@acm.org> Content-Language: en-US From: Damien Le Moal Organization: Western Digital Research In-Reply-To: <20260323202904.1248169-3-bvanassche@acm.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2026/03/23 13:29, Bart Van Assche wrote: > Add support for configuring the maximum segment size. The maximum segment > size may be set to a value smaller than the virtual memory page size. > > 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 | 13 +++++++++++++ > drivers/block/null_blk/null_blk.h | 1 + > 2 files changed, 14 insertions(+) > > diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c > index 677ac829ef80..bf63431f6820 100644 > --- a/drivers/block/null_blk/main.c > +++ b/drivers/block/null_blk/main.c > @@ -169,6 +169,10 @@ 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 = BLK_MAX_SEGMENT_SIZE; > +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"); Maximum size of a DMA segment in bytes ? (to be consistent with the code comment describing this. "segment" alone is not clear...) > + > static unsigned int nr_devices = 1; > module_param(nr_devices, uint, 0444); > MODULE_PARM_DESC(nr_devices, "Number of devices to register"); > @@ -450,6 +454,7 @@ 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); > @@ -608,6 +613,7 @@ static struct configfs_attribute *nullb_device_attrs[] = { > &nullb_device_attr_index, > &nullb_device_attr_irqmode, > &nullb_device_attr_max_sectors, > + &nullb_device_attr_max_segment_size, > &nullb_device_attr_mbps, > &nullb_device_attr_memory_backed, > &nullb_device_attr_no_sched, > @@ -805,6 +811,7 @@ 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; > @@ -1251,6 +1258,9 @@ static blk_status_t null_transfer(struct nullb *nullb, struct page *page, > unsigned int valid_len = len; > void *p; > > + WARN_ONCE(len > dev->max_segment_size, "%u > %u\n", len, > + dev->max_segment_size); > + > p = kmap_local_page(page) + off; > if (!is_write) { > if (dev->zoned) { > @@ -1298,6 +1308,8 @@ static blk_status_t null_handle_data_transfer(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; > if (transferred_bytes + len > max_bytes) > len = max_bytes - transferred_bytes; > err = null_transfer(nullb, bvec.bv_page, len, bvec.bv_offset, > @@ -1961,6 +1973,7 @@ static int null_add_dev(struct nullb_device *dev) > .logical_block_size = dev->blocksize, > .physical_block_size = dev->blocksize, > .max_hw_sectors = dev->max_sectors, > + .max_segment_size = dev->max_segment_size, > .dma_alignment = 1, > }; > > diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h > index 6c4c4bbe7dad..43dc47789718 100644 > --- a/drivers/block/null_blk/null_blk.h > +++ b/drivers/block/null_blk/null_blk.h > @@ -93,6 +93,7 @@ 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