lightnvm: pblk: sched. metadata on write thread

At the moment, line metadata is persisted on a separate work queue, that
is kicked each time that a line is closed. The assumption when designing
this was that freeing the write thread from creating a new write request
was better than the potential impact of writes colliding on the media
(user I/O and metadata I/O). Experimentation has proven that this
assumption is wrong; collision can cause up to 25% of bandwidth and
introduce long tail latencies on the write thread, which potentially
cause user write threads to spend more time spinning to get a free entry
on the write buffer.

This patch moves the metadata logic to the write thread. When a line is
closed, remaining metadata is written in memory and is placed on a
metadata queue. The write thread then takes the metadata corresponding
to the previous line, creates the write request and schedules it to
minimize collisions on the media. Using this approach, we see that we
can saturate the media's bandwidth, which helps reducing both write
latencies and the spinning time for user writer threads.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <matias@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 7 insertions, 6 deletions

diff --git a/drivers/lightnvm/pblk-map.c b/drivers/lightnvm/pblk-map.c
index 84309bd400d5..08580a649499 100644
--- a/drivers/lightnvm/pblk-map.c
+++ b/drivers/lightnvm/pblk-map.c
@@ -25,9 +25,9 @@ static void pblk_map_page_data(struct pblk *pblk, unsigned int sentry,
 			       unsigned int valid_secs)
 {
 	struct pblk_line *line = pblk_line_get_data(pblk);
-	struct line_emeta *emeta = line->emeta;
+	struct pblk_emeta *emeta = line->emeta;
 	struct pblk_w_ctx *w_ctx;
-	__le64 *lba_list = pblk_line_emeta_to_lbas(emeta);
+	__le64 *lba_list = emeta_to_lbas(pblk, emeta->buf);
 	u64 paddr;
 	int nr_secs = pblk->min_write_pgs;
 	int i;
@@ -51,7 +51,7 @@ static void pblk_map_page_data(struct pblk *pblk, unsigned int sentry,
 			w_ctx->ppa = ppa_list[i];
 			meta_list[i].lba = cpu_to_le64(w_ctx->lba);
 			lba_list[paddr] = cpu_to_le64(w_ctx->lba);
-			le64_add_cpu(&line->emeta->nr_valid_lbas, 1);
+			line->nr_valid_lbas++;
 		} else {
 			u64 addr_empty = cpu_to_le64(ADDR_EMPTY);
 
@@ -61,9 +61,11 @@ static void pblk_map_page_data(struct pblk *pblk, unsigned int sentry,
 	}
 
 	if (pblk_line_is_full(line)) {
+		struct pblk_line *prev_line = line;
 		line = pblk_line_replace_data(pblk);
 		if (!line)
 			return;
+		pblk_line_close_meta(pblk, prev_line);
 	}
 
 	pblk_down_rq(pblk, ppa_list, nr_secs, lun_bitmap);
@@ -104,11 +106,10 @@ void pblk_map_erase_rq(struct pblk *pblk, struct nvm_rq *rqd,
 		pblk_map_page_data(pblk, sentry + i, &rqd->ppa_list[i],
 					lun_bitmap, &meta_list[i], map_secs);
 
-		erase_lun = rqd->ppa_list[i].g.lun * geo->nr_chnls +
-							rqd->ppa_list[i].g.ch;
-
 		/* line can change after page map */
 		e_line = pblk_line_get_erase(pblk);
+		erase_lun = pblk_ppa_to_pos(geo, rqd->ppa_list[i]);
+
 		spin_lock(&e_line->lock);
 		if (!test_bit(erase_lun, e_line->erase_bitmap)) {
 			set_bit(erase_lun, e_line->erase_bitmap);