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Message-ID: <5166cbf7-2680-4f84-9dee-aa214862f2a8@nvidia.com>
Date: Wed, 24 Apr 2024 05:03:50 +0000
From: Chaitanya Kulkarni <chaitanyak@...dia.com>
To: Dongsheng Yang <dongsheng.yang@...ystack.cn>, "dan.j.williams@...el.com"
<dan.j.williams@...el.com>, "axboe@...nel.dk" <axboe@...nel.dk>
CC: "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>, Dongsheng Yang
<dongsheng.yang.linux@...il.com>
Subject: Re: [PATCH 5/7] cbd: introuce cbd_backend
> +
> +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
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