This is a note to let you know that I've just added the patch titled
md/raid1: fix read balance when a drive is write-mostly.
to the 3.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
md-raid1-fix-read-balance-when-a-drive-is-write-mostly.patch
and it can be found in the queue-3.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From d1901ef099c38afd11add4cfb3312c02ef21ec4a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tom=C3=A1=C5=A1=20Hodek?= <tomas.hodek@xxxxxxxx>
Date: Mon, 23 Feb 2015 11:00:38 +1100
Subject: md/raid1: fix read balance when a drive is write-mostly.
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From: =?UTF-8?q?Tom=C3=A1=C5=A1=20Hodek?= <tomas.hodek@xxxxxxxx>
commit d1901ef099c38afd11add4cfb3312c02ef21ec4a upstream.
When a drive is marked write-mostly it should only be the
target of reads if there is no other option.
This behaviour was broken by
commit 9dedf60313fa4dddfd5b9b226a0ef12a512bf9dc
md/raid1: read balance chooses idlest disk for SSD
which causes a write-mostly device to be *preferred* is some cases.
Restore correct behaviour by checking and setting
best_dist_disk and best_pending_disk rather than best_disk.
We only need to test one of these as they are both changed
from -1 or >=0 at the same time.
As we leave min_pending and best_dist unchanged, any non-write-mostly
device will appear better than the write-mostly device.
Reported-by: Tomáš Hodek <tomas.hodek@xxxxxxxx>
Reported-by: Dark Penguin <darkpenguin@xxxxxxxxx>
Signed-off-by: NeilBrown <neilb@xxxxxxx>
Link: http://marc.info/?l=linux-raid&m=135982797322422
Fixes: 9dedf60313fa4dddfd5b9b226a0ef12a512bf9dc
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/md/raid1.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -560,7 +560,7 @@ static int read_balance(struct r1conf *c
if (test_bit(WriteMostly, &rdev->flags)) {
/* Don't balance among write-mostly, just
* use the first as a last resort */
- if (best_disk < 0) {
+ if (best_dist_disk < 0) {
if (is_badblock(rdev, this_sector, sectors,
&first_bad, &bad_sectors)) {
if (first_bad < this_sector)
@@ -569,7 +569,8 @@ static int read_balance(struct r1conf *c
best_good_sectors = first_bad - this_sector;
} else
best_good_sectors = sectors;
- best_disk = disk;
+ best_dist_disk = disk;
+ best_pending_disk = disk;
}
continue;
}
Patches currently in stable-queue which might be from tomas.hodek@xxxxxxxx are
queue-3.19/md-raid1-fix-read-balance-when-a-drive-is-write-mostly.patch
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