[PATCH 2/2] lightnvm: pblk: take write semaphore on metadata

From: "Javier González" <javier@javigon.com>
To: mb@lightnvm.io
Cc: axboe@kernel.dk, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	"Javier González" <javier@cnexlabs.com>
Subject: [PATCH 2/2] lightnvm: pblk: take write semaphore on metadata
Date: Fri, 17 Aug 2018 12:19:10 +0200	[thread overview]
Message-ID: <1534501150-11906-3-git-send-email-javier@cnexlabs.com> (raw)
In-Reply-To: <1534501150-11906-1-git-send-email-javier@cnexlabs.com>

pblk guarantees write ordering at a chunk level through a per open chunk
semaphore. At this point, since we only have an open I/O stream for both
user and GC data, the semaphore is per parallel unit.

For the metadata I/O that is synchronous, the semaphore is not needed as
ordering is guaranteed. However, if the metadata scheme changes or
multiple streams are open, this guarantee might not be preserved.

This patch makes sure that all writes go through the semaphore, even for
synchronous I/O. This is consistent with pblk's write I/O model. It also
simplifies maintenance since changes in the metadata scheme could cause
ordering issues.

Signed-off-by: Javier González <javier@cnexlabs.com>
---
 drivers/lightnvm/pblk-core.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/lightnvm/pblk-core.c b/drivers/lightnvm/pblk-core.c
index 52306573cc0e..eac5bd551860 100644
--- a/drivers/lightnvm/pblk-core.c
+++ b/drivers/lightnvm/pblk-core.c
@@ -493,6 +493,20 @@ int pblk_submit_io_sync(struct pblk *pblk, struct nvm_rq *rqd)
 	return nvm_submit_io_sync(dev, rqd);
 }
 
+int pblk_submit_io_sync_sem(struct pblk *pblk, struct nvm_rq *rqd)
+{
+	struct ppa_addr *ppa_list;
+	int ret;
+
+	ppa_list = (rqd->nr_ppas > 1) ? rqd->ppa_list : &rqd->ppa_addr;
+
+	pblk_down_page(pblk, ppa_list, rqd->nr_ppas);
+	ret = pblk_submit_io_sync(pblk, rqd);
+	pblk_up_page(pblk, ppa_list, rqd->nr_ppas);
+
+	return ret;
+}
+
 static void pblk_bio_map_addr_endio(struct bio *bio)
 {
 	bio_put(bio);
@@ -731,7 +745,7 @@ static int pblk_line_smeta_write(struct pblk *pblk, struct pblk_line *line,
 		meta_list[i].lba = lba_list[paddr] = addr_empty;
 	}
 
-	ret = pblk_submit_io_sync(pblk, &rqd);
+	ret = pblk_submit_io_sync_sem(pblk, &rqd);
 	if (ret) {
 		pblk_err(pblk, "smeta I/O submission failed: %d\n", ret);
 		bio_put(bio);
-- 
2.7.4

