On Thu, Mar 14, 2019 at 9:07 AM Igor Konopko <igor.j.konopko@xxxxxxxxx> wrote:
>
> This patch changes the approach to handling partial read path.
>
> In old approach merging of data from round buffer and drive was fully
> made by drive. This had some disadvantages - code was complex and
> relies on bio internals, so it was hard to maintain and was strongly
> dependent on bio changes.
>
> In new approach most of the handling is done mostly by block layer
> functions such as bio_split(), bio_chain() and generic_make request()
> and generally is less complex and easier to maintain. Below some more
> details of the new approach.
>
> When read bio arrives, it is cloned for pblk internal purposes. All
> the L2P mapping, which includes copying data from round buffer to bio
> and thus bio_advance() calls is done on the cloned bio, so the original
> bio is untouched. Later if we found that we have partial read case, we
> still have original bio untouched, so we can split it and continue to
> process only first 4K of it in current context, when the rest will be
> called as separate bio request which is passed to generic_make_request()
> for further processing.
>
> Signed-off-by: Igor Konopko <igor.j.konopko@xxxxxxxxx>
> ---
> drivers/lightnvm/pblk-read.c | 242 ++++++++-----------------------------------
> drivers/lightnvm/pblk.h | 12 ---
> 2 files changed, 41 insertions(+), 213 deletions(-)
>
> diff --git a/drivers/lightnvm/pblk-read.c b/drivers/lightnvm/pblk-read.c
> index 6569746..54422a2 100644
> --- a/drivers/lightnvm/pblk-read.c
> +++ b/drivers/lightnvm/pblk-read.c
> @@ -222,171 +222,6 @@ static void pblk_end_io_read(struct nvm_rq *rqd)
> __pblk_end_io_read(pblk, rqd, true);
> }
>
> -static void pblk_end_partial_read(struct nvm_rq *rqd)
> -{
> - struct pblk *pblk = rqd->private;
> - struct pblk_g_ctx *r_ctx = nvm_rq_to_pdu(rqd);
> - struct pblk_pr_ctx *pr_ctx = r_ctx->private;
> - struct pblk_sec_meta *meta;
> - struct bio *new_bio = rqd->bio;
> - struct bio *bio = pr_ctx->orig_bio;
> - struct bio_vec src_bv, dst_bv;
> - void *meta_list = rqd->meta_list;
> - int bio_init_idx = pr_ctx->bio_init_idx;
> - unsigned long *read_bitmap = pr_ctx->bitmap;
> - int nr_secs = pr_ctx->orig_nr_secs;
> - int nr_holes = nr_secs - bitmap_weight(read_bitmap, nr_secs);
> - void *src_p, *dst_p;
> - int hole, i;
> -
> - if (unlikely(nr_holes == 1)) {
> - struct ppa_addr ppa;
> -
> - ppa = rqd->ppa_addr;
> - rqd->ppa_list = pr_ctx->ppa_ptr;
> - rqd->dma_ppa_list = pr_ctx->dma_ppa_list;
> - rqd->ppa_list[0] = ppa;
> - }
> -
> - for (i = 0; i < nr_secs; i++) {
> - meta = pblk_get_meta(pblk, meta_list, i);
> - pr_ctx->lba_list_media[i] = le64_to_cpu(meta->lba);
> - meta->lba = cpu_to_le64(pr_ctx->lba_list_mem[i]);
> - }
> -
> - /* Fill the holes in the original bio */
> - i = 0;
> - hole = find_first_zero_bit(read_bitmap, nr_secs);
> - do {
> - struct pblk_line *line;
> -
> - line = pblk_ppa_to_line(pblk, rqd->ppa_list[i]);
> - kref_put(&line->ref, pblk_line_put);
> -
> - meta = pblk_get_meta(pblk, meta_list, hole);
> - meta->lba = cpu_to_le64(pr_ctx->lba_list_media[i]);
> -
> - src_bv = new_bio->bi_io_vec[i++];
> - dst_bv = bio->bi_io_vec[bio_init_idx + hole];
> -
> - src_p = kmap_atomic(src_bv.bv_page);
> - dst_p = kmap_atomic(dst_bv.bv_page);
> -
> - memcpy(dst_p + dst_bv.bv_offset,
> - src_p + src_bv.bv_offset,
> - PBLK_EXPOSED_PAGE_SIZE);
> -
> - kunmap_atomic(src_p);
> - kunmap_atomic(dst_p);
> -
> - mempool_free(src_bv.bv_page, &pblk->page_bio_pool);
> -
> - hole = find_next_zero_bit(read_bitmap, nr_secs, hole + 1);
> - } while (hole < nr_secs);
> -
> - bio_put(new_bio);
> - kfree(pr_ctx);
> -
> - /* restore original request */
> - rqd->bio = NULL;
> - rqd->nr_ppas = nr_secs;
> -
> - pblk_end_user_read(bio, rqd->error);
> - __pblk_end_io_read(pblk, rqd, false);
> -}
> -
> -static int pblk_setup_partial_read(struct pblk *pblk, struct nvm_rq *rqd,
> - unsigned int bio_init_idx,
> - unsigned long *read_bitmap,
> - int nr_holes)
> -{
> - void *meta_list = rqd->meta_list;
> - struct pblk_g_ctx *r_ctx = nvm_rq_to_pdu(rqd);
> - struct pblk_pr_ctx *pr_ctx;
> - struct bio *new_bio, *bio = r_ctx->private;
> - int nr_secs = rqd->nr_ppas;
> - int i;
> -
> - new_bio = bio_alloc(GFP_KERNEL, nr_holes);
> -
> - if (pblk_bio_add_pages(pblk, new_bio, GFP_KERNEL, nr_holes))
> - goto fail_bio_put;
> -
> - if (nr_holes != new_bio->bi_vcnt) {
> - WARN_ONCE(1, "pblk: malformed bio\n");
> - goto fail_free_pages;
> - }
> -
> - pr_ctx = kzalloc(sizeof(struct pblk_pr_ctx), GFP_KERNEL);
> - if (!pr_ctx)
> - goto fail_free_pages;
> -
> - for (i = 0; i < nr_secs; i++) {
> - struct pblk_sec_meta *meta = pblk_get_meta(pblk, meta_list, i);
> -
> - pr_ctx->lba_list_mem[i] = le64_to_cpu(meta->lba);
> - }
> -
> - new_bio->bi_iter.bi_sector = 0; /* internal bio */
> - bio_set_op_attrs(new_bio, REQ_OP_READ, 0);
> -
> - rqd->bio = new_bio;
> - rqd->nr_ppas = nr_holes;
> -
> - pr_ctx->orig_bio = bio;
> - bitmap_copy(pr_ctx->bitmap, read_bitmap, NVM_MAX_VLBA);
> - pr_ctx->bio_init_idx = bio_init_idx;
> - pr_ctx->orig_nr_secs = nr_secs;
> - r_ctx->private = pr_ctx;
> -
> - if (unlikely(nr_holes == 1)) {
> - pr_ctx->ppa_ptr = rqd->ppa_list;
> - pr_ctx->dma_ppa_list = rqd->dma_ppa_list;
> - rqd->ppa_addr = rqd->ppa_list[0];
> - }
> - return 0;
> -
> -fail_free_pages:
> - pblk_bio_free_pages(pblk, new_bio, 0, new_bio->bi_vcnt);
> -fail_bio_put:
> - bio_put(new_bio);
> -
> - return -ENOMEM;
> -}
> -
> -static int pblk_partial_read_bio(struct pblk *pblk, struct nvm_rq *rqd,
> - unsigned int bio_init_idx,
> - unsigned long *read_bitmap, int nr_secs)
> -{
> - int nr_holes;
> - int ret;
> -
> - nr_holes = nr_secs - bitmap_weight(read_bitmap, nr_secs);
> -
> - if (pblk_setup_partial_read(pblk, rqd, bio_init_idx, read_bitmap,
> - nr_holes))
> - return NVM_IO_ERR;
> -
> - rqd->end_io = pblk_end_partial_read;
> -
> - ret = pblk_submit_io(pblk, rqd);
> - if (ret) {
> - bio_put(rqd->bio);
> - pblk_err(pblk, "partial read IO submission failed\n");
> - goto err;
> - }
> -
> - return NVM_IO_OK;
> -
> -err:
> - pblk_err(pblk, "failed to perform partial read\n");
> -
> - /* Free allocated pages in new bio */
> - pblk_bio_free_pages(pblk, rqd->bio, 0, rqd->bio->bi_vcnt);
> - __pblk_end_io_read(pblk, rqd, false);
> - return NVM_IO_ERR;
> -}
> -
> static void pblk_read_rq(struct pblk *pblk, struct nvm_rq *rqd, struct bio *bio,
> sector_t lba, unsigned long *read_bitmap)
> {
> @@ -432,11 +267,11 @@ int pblk_submit_read(struct pblk *pblk, struct bio *bio)
> {
> struct nvm_tgt_dev *dev = pblk->dev;
> struct request_queue *q = dev->q;
> + struct bio *split_bio, *int_bio;
> sector_t blba = pblk_get_lba(bio);
> unsigned int nr_secs = pblk_get_secs(bio);
> struct pblk_g_ctx *r_ctx;
> struct nvm_rq *rqd;
> - unsigned int bio_init_idx;
> DECLARE_BITMAP(read_bitmap, NVM_MAX_VLBA);
> int ret = NVM_IO_ERR;
>
> @@ -456,61 +291,66 @@ int pblk_submit_read(struct pblk *pblk, struct bio *bio)
> r_ctx = nvm_rq_to_pdu(rqd);
> r_ctx->start_time = jiffies;
> r_ctx->lba = blba;
> - r_ctx->private = bio; /* original bio */
>
> - /* Save the index for this bio's start. This is needed in case
> - * we need to fill a partial read.
> + /* Clone read bio to deal with:
> + * -usage of bio_advance() when memcpy data from round buffer
> + * -read errors in case of reading from device
> */
> - bio_init_idx = pblk_get_bi_idx(bio);
> + int_bio = bio_clone_fast(bio, GFP_KERNEL, &pblk_bio_set);
> + if (!int_bio)
> + return NVM_IO_ERR;
>
> if (pblk_alloc_rqd_meta(pblk, rqd))
> goto fail_rqd_free;
>
> if (nr_secs > 1)
> - pblk_read_ppalist_rq(pblk, rqd, bio, blba, read_bitmap);
> + pblk_read_ppalist_rq(pblk, rqd, int_bio, blba, read_bitmap);
> else
> - pblk_read_rq(pblk, rqd, bio, blba, read_bitmap);
> + pblk_read_rq(pblk, rqd, int_bio, blba, read_bitmap);
> +
> +split_retry:
> + r_ctx->private = bio; /* original bio */
>
> - if (bitmap_full(read_bitmap, nr_secs)) {
> + if (bitmap_full(read_bitmap, rqd->nr_ppas)) {
> + bio_put(int_bio);
> atomic_inc(&pblk->inflight_io);
> __pblk_end_io_read(pblk, rqd, false);
> return NVM_IO_DONE;
> }
>
> - /* All sectors are to be read from the device */
> - if (bitmap_empty(read_bitmap, rqd->nr_ppas)) {
> - struct bio *int_bio = NULL;
> + if (!bitmap_empty(read_bitmap, rqd->nr_ppas)) {
> + /* The read bio request could be partially filled by the write
> + * buffer, but there are some holes that need to be read from
> + * the drive. In order to handle this, we will use block layer
> + * mechanism to split this request in to smaller ones.
> + */
> + split_bio = bio_split(bio, NR_PHY_IN_LOG, GFP_KERNEL,
> + &pblk_bio_set);
This is quite inefficient. If you have an rqd with 63 sectors on the device and
the 64th is cached, you are splitting 63 times whereas a single split
would be sufficient.
> + bio_chain(split_bio, bio);
I am not sure if it's needed but in blk_queue_split() these flags are set
before making the request:
split->bi_opf |= REQ_NOMERGE;
bio_set_flag(*bio, BIO_QUEUE_ENTERED);
> + generic_make_request(bio);
pblk_lookup_l2p_seq() increments line->ref. You have to release the krefs before
requeing the request.
You might consider introducing a pblk_lookup_l2p_uncached() which returns when
it finds a cached sector and returns its index. Doing so you can avoid obtaining
superfluous line->refs and we could also get rid of the read_bitmap
entirely. This
index could also be used to split the bio at the right position.
> +
> + /* Retry after split with new bio and existing rqd */
> + bio = split_bio;
> + rqd->nr_ppas = 1;
> + rqd->ppa_addr = rqd->ppa_list[0];
>
> - /* Clone read bio to deal with read errors internally */
> + /* Recreate int_bio for the retry needs */
> + bio_put(int_bio);
> int_bio = bio_clone_fast(bio, GFP_KERNEL, &pblk_bio_set);
> - if (!int_bio) {
> - pblk_err(pblk, "could not clone read bio\n");
> - goto fail_end_io;
> - }
> -
> - rqd->bio = int_bio;
> -
> - if (pblk_submit_io(pblk, rqd)) {
> - pblk_err(pblk, "read IO submission failed\n");
> - ret = NVM_IO_ERR;
> - goto fail_end_io;
> - }
> -
> - return NVM_IO_OK;
> + if (!int_bio)
> + return NVM_IO_ERR;
> + goto split_retry;
> }
>
> - /* The read bio request could be partially filled by the write buffer,
> - * but there are some holes that need to be read from the drive.
> - */
> - ret = pblk_partial_read_bio(pblk, rqd, bio_init_idx, read_bitmap,
> - nr_secs);
> - if (ret)
> - goto fail_meta_free;
> -
> + /* All sectors are to be read from the device */
> + rqd->bio = int_bio;
> + if (pblk_submit_io(pblk, rqd)) {
> + pblk_err(pblk, "read IO submission failed\n");
> + ret = NVM_IO_ERR;
> + goto fail_end_io;
> + }
> return NVM_IO_OK;
>
> -fail_meta_free:
> - nvm_dev_dma_free(dev->parent, rqd->meta_list, rqd->dma_meta_list);
> fail_rqd_free:
> pblk_free_rqd(pblk, rqd, PBLK_READ);
> return ret;
> diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
> index 381f074..0a85990 100644
> --- a/drivers/lightnvm/pblk.h
> +++ b/drivers/lightnvm/pblk.h
> @@ -123,18 +123,6 @@ struct pblk_g_ctx {
> u64 lba;
> };
>
> -/* partial read context */
> -struct pblk_pr_ctx {
> - struct bio *orig_bio;
> - DECLARE_BITMAP(bitmap, NVM_MAX_VLBA);
> - unsigned int orig_nr_secs;
> - unsigned int bio_init_idx;
> - void *ppa_ptr;
> - dma_addr_t dma_ppa_list;
> - u64 lba_list_mem[NVM_MAX_VLBA];
> - u64 lba_list_media[NVM_MAX_VLBA];
> -};
> -
> /* Pad context */
> struct pblk_pad_rq {
> struct pblk *pblk;
> --
> 2.9.5
>
