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From: Chaitanya Kulkarni <chaitanyak@nvidia.com>
To: Dongsheng Yang <dongsheng.yang@easystack.cn>,
	"dan.j.williams@intel.com" <dan.j.williams@intel.com>,
	"axboe@kernel.dk" <axboe@kernel.dk>
Cc: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-cxl@vger.kernel.org" <linux-cxl@vger.kernel.org>,
	Dongsheng Yang <dongsheng.yang.linux@gmail.com>
Subject: Re: [PATCH 5/7] cbd: introuce cbd_backend
Date: Wed, 24 Apr 2024 05:03:50 +0000	[thread overview]
Message-ID: <5166cbf7-2680-4f84-9dee-aa214862f2a8@nvidia.com> (raw)
In-Reply-To: <20240422071606.52637-6-dongsheng.yang@easystack.cn>

> +
> +struct cbd_backend_io {
> +	struct cbd_se		*se;
> +	u64			off;
> +	u32			len;
> +	struct bio		*bio;
> +	struct cbd_handler	*handler;
> +};
> +

why not use inline bvecs and avoid bio page allocation for reasonable
size ? instead of performing the allocation for each request ...

> +static inline void complete_cmd(struct cbd_handler *handler, u64 priv_data, int ret)
> +{
> +	struct cbd_ce *ce = get_compr_head(handler);
> +
> +	memset(ce, 0, sizeof(*ce));
> +	ce->priv_data = priv_data;
> +	ce->result = ret;
> +	CBDC_UPDATE_COMPR_HEAD(handler->channel_info->compr_head,
> +			       sizeof(struct cbd_ce),
> +			       handler->channel_info->compr_size);
> +
> +	cbdc_flush_ctrl(&handler->channel);
> +
> +	return;
> +}
> +
> +static void backend_bio_end(struct bio *bio)
> +{
> +	struct cbd_backend_io *backend_io = bio->bi_private;
> +	struct cbd_se *se = backend_io->se;
> +	struct cbd_handler *handler = backend_io->handler;
> +
> +	if (bio->bi_status == 0 &&
> +	    cbd_se_hdr_get_op(se->header.len_op) == CBD_OP_READ) {
> +		cbdc_copy_from_bio(&handler->channel, se->data_off, se->data_len, bio);
> +	}
> +
> +	complete_cmd(handler, se->priv_data, bio->bi_status);
> +
> +	bio_free_pages(bio);
> +	bio_put(bio);
> +	kfree(backend_io);
> +}
> +
> +static int cbd_bio_alloc_pages(struct bio *bio, size_t size, gfp_t gfp_mask)
> +{
> +	int ret = 0;
> +
> +        while (size) {
> +                struct page *page = alloc_pages(gfp_mask, 0);
> +                unsigned len = min_t(size_t, PAGE_SIZE, size);

alloc_page() call should be close to below check ..

> +
> +                if (!page) {
> +			pr_err("failed to alloc page");
> +			ret = -ENOMEM;
> +			break;
> +		}
> +
> +		ret = bio_add_page(bio, page, len, 0);
> +                if (unlikely(ret != len)) {
> +                        __free_page(page);
> +			pr_err("failed to add page");
> +                        break;
> +                }
> +
> +                size -= len;
> +        }
> +
> +	if (size)
> +		bio_free_pages(bio);
> +	else
> +		ret = 0;
> +
> +        return ret;
> +}

code formatting seems to be broken for above function plz check..

> +
> +static struct cbd_backend_io *backend_prepare_io(struct cbd_handler *handler, struct cbd_se *se, blk_opf_t opf)
> +{
> +	struct cbd_backend_io *backend_io;
> +	struct cbd_backend *cbdb = handler->cbdb;
> +
> +	backend_io = kzalloc(sizeof(struct cbd_backend_io), GFP_KERNEL);

will above allocation always succeed ? or NULL check should be here ?

> +	backend_io->se = se;
> +
> +	backend_io->handler = handler;
> +	backend_io->bio = bio_alloc_bioset(cbdb->bdev, roundup(se->len, 4096) / 4096, opf, GFP_KERNEL, &handler->bioset);
> +
> +	backend_io->bio->bi_iter.bi_sector = se->offset >> SECTOR_SHIFT;
> +	backend_io->bio->bi_iter.bi_size = 0;
> +	backend_io->bio->bi_private = backend_io;
> +	backend_io->bio->bi_end_io = backend_bio_end;
> +
> +	return backend_io;
> +}
> +
> +static int handle_backend_cmd(struct cbd_handler *handler, struct cbd_se *se)
> +{
> +	struct cbd_backend *cbdb = handler->cbdb;
> +	u32 len = se->len;
> +	struct cbd_backend_io *backend_io = NULL;
> +	int ret;
> +
> +	if (cbd_se_hdr_flags_test(se, CBD_SE_HDR_DONE)) {
> +		return 0 ;
> +	}
> +
> +	switch (cbd_se_hdr_get_op(se->header.len_op)) {
> +	case CBD_OP_PAD:
> +		cbd_se_hdr_flags_set(se, CBD_SE_HDR_DONE);
> +		return 0;
> +	case CBD_OP_READ:
> +		backend_io = backend_prepare_io(handler, se, REQ_OP_READ);
> +		break;
> +	case CBD_OP_WRITE:
> +		backend_io = backend_prepare_io(handler, se, REQ_OP_WRITE);
> +		break;
> +	case CBD_OP_DISCARD:
> +		ret = blkdev_issue_discard(cbdb->bdev, se->offset >> SECTOR_SHIFT,
> +				se->len, GFP_NOIO);

any specific reason to not use GFP_KERNEL ?

> +		goto complete_cmd;
> +	case CBD_OP_WRITE_ZEROS:
> +		ret = blkdev_issue_zeroout(cbdb->bdev, se->offset >> SECTOR_SHIFT,
> +				se->len, GFP_NOIO, 0);

any specific reason to not use GFP_KERNEL ?

> +		goto complete_cmd;
> +	case CBD_OP_FLUSH:
> +		ret = blkdev_issue_flush(cbdb->bdev);
> +		goto complete_cmd;
> +	default:
> +		pr_err("unrecognized op: %x", cbd_se_hdr_get_op(se->header.len_op));
> +		ret = -EIO;
> +		goto complete_cmd;
> +	}
> +
> +	if (!backend_io)
> +		return -ENOMEM;

there is no NULL check in the backend_prepare_io() not sure about
above condition in current code unless you return NULL ...

> +
> +	ret = cbd_bio_alloc_pages(backend_io->bio, len, GFP_NOIO);
> +	if (ret) {
> +		kfree(backend_io);
> +		return ret;
> +	}
> +
> +	if (cbd_se_hdr_get_op(se->header.len_op) == CBD_OP_WRITE) {
> +		cbdc_copy_to_bio(&handler->channel, se->data_off, se->data_len, backend_io->bio);
> +	}
> +
> +	submit_bio(backend_io->bio);
> +

unless I didn't understand the code, you are building a single bio from
incoming request, that might not have enough space to accommodate all
the data from incoming request, hence you are returning an error from
cbd_bio_alloc_pages() when bio_add_page() fail ...

bio_add_page() can fail for multiple reasons, instead of trying to
build only one bio that might be smaller for the size of the I/O and
returning error, why not use the chain of the small size bios ? that
way you will not run out of the space in single bio and still finish
the I/O by avoiding bio_add_page() failure that might happen due to
bio full ?

> +	return 0;
> +
> +complete_cmd:
> +	complete_cmd(handler, se->priv_data, ret);
> +	return 0;
> +}
> +
> +static void handle_work_fn(struct work_struct *work)
> +{
> +	struct cbd_handler *handler = container_of(work, struct cbd_handler, handle_work.work);
> +	struct cbd_se *se;
> +	int ret;
> +again:
> +	/* channel ctrl would be updated by blkdev queue */
> +	cbdc_flush_ctrl(&handler->channel);
> +	se = get_se_to_handle(handler);
> +	if (se == get_se_head(handler)) {
> +		if (cbdwc_need_retry(&handler->handle_worker_cfg)) {
> +			goto again;
> +		}
> +
> +		cbdwc_miss(&handler->handle_worker_cfg);
> +
> +		queue_delayed_work(handler->handle_wq, &handler->handle_work, usecs_to_jiffies(0));
> +		return;
> +	}
> +
> +	cbdwc_hit(&handler->handle_worker_cfg);
> +	cbdt_flush_range(handler->cbdb->cbdt, se, sizeof(*se));
> +	ret = handle_backend_cmd(handler, se);
> +	if (!ret) {
> +		/* this se is handled */
> +		handler->se_to_handle = (handler->se_to_handle + cbd_se_hdr_get_len(se->header.len_op)) % handler->channel_info->cmdr_size;

this is a really long line, if possible keep code under 80 char, I know
it's not a requirement anymore but it will match block drivers ..

-ck



  reply	other threads:[~2024-04-24  5:03 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-04-22  7:15 [PATCH RFC 0/7] block: Introduce CBD (CXL Block Device) Dongsheng Yang
2024-04-22  7:16 ` [PATCH 1/7] block: Init for CBD(CXL " Dongsheng Yang
2024-04-22 18:39   ` Randy Dunlap
2024-04-22 22:41     ` Dongsheng Yang
2024-04-24  3:58   ` Chaitanya Kulkarni
2024-04-24  8:36     ` Dongsheng Yang
2024-04-22  7:16 ` [PATCH 2/7] cbd: introduce cbd_transport Dongsheng Yang
2024-04-24  4:08   ` Chaitanya Kulkarni
2024-04-24  8:43     ` Dongsheng Yang
2024-04-22  7:16 ` [PATCH 3/7] cbd: introduce cbd_channel Dongsheng Yang
2024-04-22  7:16 ` [PATCH 4/7] cbd: introduce cbd_host Dongsheng Yang
2024-04-25  5:51   ` [EXTERNAL] " Bharat Bhushan
2024-04-22  7:16 ` [PATCH 5/7] cbd: introuce cbd_backend Dongsheng Yang
2024-04-24  5:03   ` Chaitanya Kulkarni [this message]
2024-04-24  8:36     ` Dongsheng Yang
2024-04-25  5:46   ` [EXTERNAL] " Bharat Bhushan
2024-04-22  7:16 ` [PATCH 7/7] cbd: add related sysfs files in transport register Dongsheng Yang
2024-04-25  5:24   ` [EXTERNAL] " Bharat Bhushan
2024-04-22 22:42 ` [PATCH 6/7] cbd: introduce cbd_blkdev Dongsheng Yang
2024-04-23  7:27   ` Dongsheng Yang
2024-04-24  4:29 ` [PATCH RFC 0/7] block: Introduce CBD (CXL Block Device) Dan Williams
2024-04-24  6:33   ` Dongsheng Yang
2024-04-24 15:14     ` Gregory Price
2024-04-26  1:25       ` Dongsheng Yang
2024-04-26 13:48         ` Gregory Price
2024-04-26 14:53           ` Dongsheng Yang
2024-04-26 16:14             ` Gregory Price
2024-04-28  5:47               ` Dongsheng Yang
2024-04-28 16:44                 ` Gregory Price
2024-04-28 16:55                 ` John Groves
2024-05-03  9:52                   ` Jonathan Cameron
2024-05-08 11:39                     ` Dongsheng Yang
2024-05-08 12:11                       ` Jonathan Cameron
2024-05-08 13:03                         ` Dongsheng Yang
2024-05-08 15:44                           ` Jonathan Cameron
2024-05-09 11:24                             ` Dongsheng Yang
2024-05-09 12:21                               ` Jonathan Cameron
2024-05-09 13:03                                 ` Dongsheng Yang
2024-05-21 18:41                                   ` Dan Williams
2024-05-22  6:17                                     ` Dongsheng Yang
2024-05-29 15:25                                       ` Gregory Price
2024-05-30  6:59                                         ` Dongsheng Yang
2024-05-30 13:38                                           ` Jonathan Cameron
2024-06-01  3:22                                             ` Dan Williams
2024-06-03 12:48                                               ` Jonathan Cameron
2024-06-03 17:28                                                 ` James Morse
2024-06-04 14:26                                                   ` Jonathan Cameron
2024-05-31 14:23                                           ` Gregory Price
2024-06-03  1:33                                             ` Dongsheng Yang
2024-04-30  0:34                 ` Dan Williams
2024-04-24 18:08     ` Dan Williams
     [not found]       ` <539c1323-68f9-d753-a102-692b69049c20@easystack.cn>
2024-04-30  0:10         ` Dan Williams

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