[RFC PATCH 4/5] md/raid1: use rot policy when no nonrot disk is readable
From: Chen Cheng <hidden>
Date: 2026-08-18 07:07:19
Also in:
lkml
Subsystem:
software raid (multiple disks) support, the rest · Maintainers:
Song Liu, Yu Kuai, Linus Torvalds
From: Chen Cheng <redacted> has_nonrot selects mixed policy or rot-only policy. Current: 1. has_nonrot is true if conf->nonrot_disks > 0. 2. nonrot_disks counts every nonrot disk. 3. A Faulty disk, a rebuild disk, and a WriteMostly disk still count. Problem: 1. The array is NVMe + HDD. The NVMe fails. Only the HDD can take reads. 2. nonrot_disks is still 1. The code thinks this is a mixed array. 3. Sequential reads on the HDD do not stay on the HDD. Mixed policy will not keep a rot disk. 4. Every read still advances the nonrot round-robin, though no nonrot disk can take the read. Improve: 1. Look at disks that can take this read. 2. If none of them is nonrot, use the rot-only policy. Signed-off-by: Chen Cheng <redacted> --- drivers/md/raid1.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 523b55d42779..f476d4dea4be 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c@@ -793,10 +793,28 @@ struct read_balance_ctl { static int raid1_rr_pos(int disk, int start, int n) { return ((disk % n) - start + n) % n; } +static bool raid1_has_readable_nonrot(struct r1conf *conf, + struct r1bio *r1_bio) +{ + int disk; + + for (disk = 0; disk < conf->raid_disks * 2; disk++) { + struct md_rdev *rdev; + + if (r1_bio->bios[disk] == IO_BLOCKED) + continue; + rdev = conf->mirrors[disk].rdev; + if (rdev_readable(rdev, r1_bio) && + test_bit(Nonrot, &rdev->flags)) + return true; + } + return false; +} + static bool is_better_disk(unsigned int pending, int disk, bool nonrot, const struct read_balance_ctl *ctl, int rr_start, int n) { if (ctl->min_pending_disk < 0)
@@ -814,11 +832,11 @@ static bool is_better_disk(unsigned int pending, int disk, bool nonrot, static int choose_best_rdev(struct r1conf *conf, struct r1bio *r1_bio) { int disk; int rr_start = 0; - bool has_nonrot = READ_ONCE(conf->nonrot_disks); + bool has_nonrot = raid1_has_readable_nonrot(conf, r1_bio); struct read_balance_ctl ctl = { .closest_dist_disk = -1, .closest_dist = MaxSector, .min_pending_disk = -1, .min_pending = UINT_MAX,
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2.55.0