lightnvm: pblk: simplify partial read path

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. 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 part 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 <[email protected]>
Reviewed-by: Heiner Litz <[email protected]>
Reviewed-by: Javier González <[email protected]>
Signed-off-by: Matias Bjørling <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

Author: igorkonopko

drivers/lightnvm/pblk-core.c

@@ -2147,8 +2147,8 @@ void pblk_update_map_dev(struct pblk *pblk, sector_t lba,
 	spin_unlock(&pblk->trans_lock);
 }
 
-void pblk_lookup_l2p_seq(struct pblk *pblk, struct ppa_addr *ppas,
-			 sector_t blba, int nr_secs)
+int pblk_lookup_l2p_seq(struct pblk *pblk, struct ppa_addr *ppas,
+			 sector_t blba, int nr_secs, bool *from_cache)
 {
 	int i;
 
@@ -2162,10 +2162,19 @@ void pblk_lookup_l2p_seq(struct pblk *pblk, struct ppa_addr *ppas,
 		if (!pblk_ppa_empty(ppa) && !pblk_addr_in_cache(ppa)) {
 			struct pblk_line *line = pblk_ppa_to_line(pblk, ppa);
 
+			if (i > 0 && *from_cache)
+				break;
+			*from_cache = false;
+
 			kref_get(&line->ref);
+		} else {
+			if (i > 0 && !*from_cache)
+				break;
+			*from_cache = true;
 		}
 	}
 	spin_unlock(&pblk->trans_lock);
+	return i;
 }
 
 void pblk_lookup_l2p_rand(struct pblk *pblk, struct ppa_addr *ppas,

drivers/lightnvm/pblk-rb.c

@@ -642,7 +642,7 @@ unsigned int pblk_rb_read_to_bio(struct pblk_rb *rb, struct nvm_rq *rqd,
  * be directed to disk.
  */
 int pblk_rb_copy_to_bio(struct pblk_rb *rb, struct bio *bio, sector_t lba,
-			struct ppa_addr ppa, int bio_iter, bool advanced_bio)
+			struct ppa_addr ppa)
 {
 	struct pblk *pblk = container_of(rb, struct pblk, rwb);
 	struct pblk_rb_entry *entry;
@@ -673,15 +673,6 @@ int pblk_rb_copy_to_bio(struct pblk_rb *rb, struct bio *bio, sector_t lba,
 		ret = 0;
 		goto out;
 	}
-
-	/* Only advance the bio if it hasn't been advanced already. If advanced,
-	 * this bio is at least a partial bio (i.e., it has partially been
-	 * filled with data from the cache). If part of the data resides on the
-	 * media, we will read later on
-	 */
-	if (unlikely(!advanced_bio))
-		bio_advance(bio, bio_iter * PBLK_EXPOSED_PAGE_SIZE);
-
 	data = bio_data(bio);
 	memcpy(data, entry->data, rb->seg_size);