| From | Kamal Mostafa <> | Subject | [PATCH 3.13.y-ckt 138/143] md/raid1: fix read balance when a drive is write-mostly. | Date | Tue, 31 Mar 2015 12:48:23 -0700 |
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3.13.11-ckt18 -stable review patch. If anyone has any objections, please let me know.
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From: =?UTF-8?q?Tom=C3=A1=C5=A1=20Hodek?= <tomas.hodek@volny.cz>
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@volny.cz> Reported-by: Dark Penguin <darkpenguin@yandex.ru> Signed-off-by: NeilBrown <neilb@suse.de> Link: http://marc.info/?l=linux-raid&m=135982797322422 Fixes: 9dedf60313fa4dddfd5b9b226a0ef12a512bf9dc Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- drivers/md/raid1.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c index e4885c0..53457ee 100644 --- a/drivers/md/raid1.c +++ b/drivers/md/raid1.c @@ -563,7 +563,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect 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) @@ -572,7 +572,8 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect best_good_sectors = first_bad - this_sector; } else best_good_sectors = sectors; - best_disk = disk; + best_dist_disk = disk; + best_pending_disk = disk; } continue; } -- 1.9.1
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