Re: [PATCH v8 9/9] null_blk: add support for copy offload

From: Nitesh Shetty <nj.shetty@samsung.com>
To: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Cc: Anuj Gupta <anuj20.g@samsung.com>, Jens Axboe <axboe@kernel.dk>,
	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>,
	James Smart <james.smart@broadcom.com>,
	Chaitanya Kulkarni <kch@nvidia.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christian Brauner <brauner@kernel.org>,
	bvanassche@acm.org, hare@suse.de, ming.lei@redhat.com,
	joshi.k@samsung.com, nitheshshetty@gmail.com,
	gost.dev@samsung.com, Vincent Fu <vincent.fu@samsung.com>,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v8 9/9] null_blk: add support for copy offload
Date: Wed, 29 Mar 2023 17:52:48 +0530	[thread overview]
Message-ID: <20230329122248.GD11932@green5> (raw)
In-Reply-To: <71d9f461-a708-341f-d012-d142086c026e@opensource.wdc.com>

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On Wed, Mar 29, 2023 at 06:04:49PM +0900, Damien Le Moal wrote:
> On 3/27/23 17:40, Anuj Gupta wrote:
> > From: Nitesh Shetty <nj.shetty@samsung.com>
> > 
> > Implementaion is based on existing read and write infrastructure.
> > 
> > Suggested-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
> > Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
> > Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> > Signed-off-by: Vincent Fu <vincent.fu@samsung.com>
> > ---
> >  drivers/block/null_blk/main.c     | 94 +++++++++++++++++++++++++++++++
> >  drivers/block/null_blk/null_blk.h |  7 +++
> >  2 files changed, 101 insertions(+)
> > 
> > diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
> > index 9e6b032c8ecc..84c5fbcd67a5 100644
> > --- a/drivers/block/null_blk/main.c
> > +++ b/drivers/block/null_blk/main.c
> > @@ -1257,6 +1257,81 @@ static int null_transfer(struct nullb *nullb, struct page *page,
> >  	return err;
> >  }
> >  
> > +static inline int nullb_setup_copy_read(struct nullb *nullb,
> > +		struct bio *bio)
> > +{
> > +	struct nullb_copy_token *token = bvec_kmap_local(&bio->bi_io_vec[0]);
> > +
> > +	memcpy(token->subsys, "nullb", 5);
> > +	token->sector_in = bio->bi_iter.bi_sector;
> > +	token->nullb = nullb;
> > +	token->sectors = bio->bi_iter.bi_size >> SECTOR_SHIFT;
> > +
> > +	return 0;
> > +}
> > +
> > +static inline int nullb_setup_copy_write(struct nullb *nullb,
> > +		struct bio *bio, bool is_fua)
> > +{
> > +	struct nullb_copy_token *token = bvec_kmap_local(&bio->bi_io_vec[0]);
> > +	sector_t sector_in, sector_out;
> > +	void *in, *out;
> > +	size_t rem, temp;
> > +	unsigned long offset_in, offset_out;
> > +	struct nullb_page *t_page_in, *t_page_out;
> > +	int ret = -EIO;
> > +
> > +	if (unlikely(memcmp(token->subsys, "nullb", 5)))
> > +		return -EOPNOTSUPP;
> > +	if (unlikely(token->nullb != nullb))
> > +		return -EOPNOTSUPP;
> > +	if (WARN_ON(token->sectors != bio->bi_iter.bi_size >> SECTOR_SHIFT))
> > +		return -EOPNOTSUPP;
> 
> EOPNOTSUPP is strange. These are EINVAL, no ?.
> 
acked, will update in next revision.

> > +
> > +	sector_in = token->sector_in;
> > +	sector_out = bio->bi_iter.bi_sector;
> > +	rem = token->sectors << SECTOR_SHIFT;
> > +
> > +	spin_lock_irq(&nullb->lock);
> > +	while (rem > 0) {
> > +		temp = min_t(size_t, nullb->dev->blocksize, rem);
> > +		offset_in = (sector_in & SECTOR_MASK) << SECTOR_SHIFT;
> > +		offset_out = (sector_out & SECTOR_MASK) << SECTOR_SHIFT;
> > +
> > +		if (null_cache_active(nullb) && !is_fua)
> > +			null_make_cache_space(nullb, PAGE_SIZE);
> > +
> > +		t_page_in = null_lookup_page(nullb, sector_in, false,
> > +			!null_cache_active(nullb));
> > +		if (!t_page_in)
> > +			goto err;
> > +		t_page_out = null_insert_page(nullb, sector_out,
> > +			!null_cache_active(nullb) || is_fua);
> > +		if (!t_page_out)
> > +			goto err;
> > +
> > +		in = kmap_local_page(t_page_in->page);
> > +		out = kmap_local_page(t_page_out->page);
> > +
> > +		memcpy(out + offset_out, in + offset_in, temp);
> > +		kunmap_local(out);
> > +		kunmap_local(in);
> > +		__set_bit(sector_out & SECTOR_MASK, t_page_out->bitmap);
> > +
> > +		if (is_fua)
> > +			null_free_sector(nullb, sector_out, true);
> > +
> > +		rem -= temp;
> > +		sector_in += temp >> SECTOR_SHIFT;
> > +		sector_out += temp >> SECTOR_SHIFT;
> > +	}
> > +
> > +	ret = 0;
> > +err:
> > +	spin_unlock_irq(&nullb->lock);
> > +	return ret;
> > +}
> > +
> >  static int null_handle_rq(struct nullb_cmd *cmd)
> >  {
> >  	struct request *rq = cmd->rq;
> > @@ -1267,6 +1342,14 @@ static int null_handle_rq(struct nullb_cmd *cmd)
> >  	struct req_iterator iter;
> >  	struct bio_vec bvec;
> >  
> > +	if (rq->cmd_flags & REQ_COPY) {
> > +		if (op_is_write(req_op(rq)))
> > +			return nullb_setup_copy_write(nullb, rq->bio,
> > +						rq->cmd_flags & REQ_FUA);
> > +		else
> 
> No need for this else.
> 

acked

> > +			return nullb_setup_copy_read(nullb, rq->bio);
> > +	}
> > +
> >  	spin_lock_irq(&nullb->lock);
> >  	rq_for_each_segment(bvec, rq, iter) {
> >  		len = bvec.bv_len;
> > @@ -1294,6 +1377,14 @@ static int null_handle_bio(struct nullb_cmd *cmd)
> >  	struct bio_vec bvec;
> >  	struct bvec_iter iter;
> >  
> > +	if (bio->bi_opf & REQ_COPY) {
> > +		if (op_is_write(bio_op(bio)))
> > +			return nullb_setup_copy_write(nullb, bio,
> > +							bio->bi_opf & REQ_FUA);
> > +		else
> 
> No need for this else.
> 

acked

> > +			return nullb_setup_copy_read(nullb, bio);
> > +	}
> > +
> >  	spin_lock_irq(&nullb->lock);
> >  	bio_for_each_segment(bvec, bio, iter) {
> >  		len = bvec.bv_len;
> > @@ -2146,6 +2237,9 @@ static int null_add_dev(struct nullb_device *dev)
> >  	list_add_tail(&nullb->list, &nullb_list);
> >  	mutex_unlock(&lock);
> >  
> > +	blk_queue_max_copy_sectors_hw(nullb->disk->queue, 1024);
> > +	blk_queue_flag_set(QUEUE_FLAG_COPY, nullb->disk->queue);
> 
> This should NOT be unconditionally enabled with a magic value of 1K sectors. The
> max copy sectors needs to be set with a configfs attribute so that we can
> enable/disable the copy offload support, to be able to exercise both block layer
> emulation and native device support.
> 

acked

> > +
> >  	pr_info("disk %s created\n", nullb->disk_name);
> >  
> >  	return 0;
> > diff --git a/drivers/block/null_blk/null_blk.h b/drivers/block/null_blk/null_blk.h
> > index eb5972c50be8..94e524e7306a 100644
> > --- a/drivers/block/null_blk/null_blk.h
> > +++ b/drivers/block/null_blk/null_blk.h
> > @@ -67,6 +67,13 @@ enum {
> >  	NULL_Q_MQ	= 2,
> >  };
> >  
> > +struct nullb_copy_token {
> > +	char subsys[5];
> > +	struct nullb *nullb;
> > +	u64 sector_in;
> > +	u64 sectors;
> > +};
> > +
> >  struct nullb_device {
> >  	struct nullb *nullb;
> >  	struct config_item item;
> 
> -- 
> Damien Le Moal
> Western Digital Research
> 
> 
Thank you,
Nitesh Shetty

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