linux-kernel - [PATCH] Round UBI average erase count up to next integer

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Message-Id: <20180918130521.22880-2-amworsley@gmail.com>
Date:   Tue, 18 Sep 2018 23:05:21 +1000
From:   Andrew Worsley <amworsley@...il.com>
To:     Artem Bityutskiy <dedekind1@...il.com>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Marek Vasut <marek.vasut@...il.com>,
        linux-mtd@...ts.infradead.org (open list:UNSORTED BLOCK IMAGES (UBI)),
        linux-kernel@...r.kernel.org (open list)
Cc:     Andrew Worsley <amworsley@...il.com>
Subject: [PATCH] Round UBI average erase count up to next integer

Use a slightly larger than average EC so these PEBs will be
reinitialised with erase counts that make them less likely to
be reused than other (perhaps less worn or error-prone) PEBs

We have more frequent ECC failures on reads of page 0 of some PEBs
which manifest itself commonly during ubiattach. We believe this is due to
"program disturb" and want those PEB to be re-used later than average.

Signed-off-by: Andrew Worsley <amworsley@...il.com>
---
 drivers/mtd/ubi/attach.c  | 2 +-
 drivers/mtd/ubi/fastmap.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/ubi/attach.c b/drivers/mtd/ubi/attach.c
index 93ceea4f27d5..f97e2ba56fb2 100644
--- a/drivers/mtd/ubi/attach.c
+++ b/drivers/mtd/ubi/attach.c
@@ -1414,7 +1414,7 @@ static int scan_all(struct ubi_device *ubi, struct ubi_attach_info *ai,
 
 	/* Calculate mean erase counter */
 	if (ai->ec_count)
-		ai->mean_ec = div_u64(ai->ec_sum, ai->ec_count);
+		ai->mean_ec = div_u64(ai->ec_sum+ai->ec_count-1, ai->ec_count);
 
 	err = late_analysis(ubi, ai);
 	if (err)
diff --git a/drivers/mtd/ubi/fastmap.c b/drivers/mtd/ubi/fastmap.c
index 462526a10537..91e513788f38 100644
--- a/drivers/mtd/ubi/fastmap.c
+++ b/drivers/mtd/ubi/fastmap.c
@@ -684,7 +684,7 @@ static int ubi_attach_fastmap(struct ubi_device *ubi,
 			be32_to_cpu(fmec->ec), 1);
 	}
 
-	ai->mean_ec = div_u64(ai->ec_sum, ai->ec_count);
+	ai->mean_ec = div_u64(ai->ec_sum+ai->ec_count-1, ai->ec_count);
 	ai->bad_peb_count = be32_to_cpu(fmhdr->bad_peb_count);
 
 	/* Iterate over all volumes and read their EBA table */
-- 
2.11.0