[PATCH 03/18] lightnvm: pblk: simplify partial read path

[Igor Konopko <igor.j.konopko@intel.com>]

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@intel.com>
---
 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);
+		bio_chain(split_bio, bio);
+		generic_make_request(bio);
+
+		/* 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