Re: [PATCH md-6.9 v2 02/10] md/raid1: record nonrot rdevs while adding/removing rdevs to conf

Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> · Wed, 28 Feb 2024 10:40:06 +0800

Hi,

在 2024/02/28 9:56, Xiao Ni 写道:
On Tue, Feb 27, 2024 at 8:09 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:

From: Yu Kuai <yukuai3@xxxxxxxxxx>

For raid1, each read will iterate all the rdevs from conf and check if
any rdev is non-rotational, then choose rdev with minimal IO inflight
if so, or rdev with closest distance otherwise.

Disk nonrot info can be changed through sysfs entry:

/sys/block/[disk_name]/queue/rotational

However, consider that this should only be used for testing, and user
really shouldn't do this in real life. Record the number of non-rotational
disks in conf, to avoid checking each rdev in IO fast path and simplify
read_balance() a little bit.

Co-developed-by: Paul Luse <paul.e.luse@xxxxxxxxxxxxxxx>
Signed-off-by: Paul Luse <paul.e.luse@xxxxxxxxxxxxxxx>
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
  drivers/md/md.h    |  1 +
  drivers/md/raid1.c | 17 ++++++++++-------
  drivers/md/raid1.h |  1 +
  3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/md/md.h b/drivers/md/md.h
index a49ab04ab707..b2076a165c10 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -207,6 +207,7 @@ enum flag_bits {
                                  * check if there is collision between raid1
                                  * serial bios.
                                  */
+       Nonrot,                 /* non-rotational device (SSD) */
  };

  static inline int is_badblock(struct md_rdev *rdev, sector_t s, int sectors,
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index a145fe48b9ce..0fed01b06de9 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -599,7 +599,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
         int sectors;
         int best_good_sectors;
         int best_disk, best_dist_disk, best_pending_disk;
-       int has_nonrot_disk;
         int disk;
         sector_t best_dist;
         unsigned int min_pending;
@@ -620,7 +619,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
         best_pending_disk = -1;
         min_pending = UINT_MAX;
         best_good_sectors = 0;
-       has_nonrot_disk = 0;
         choose_next_idle = 0;
         clear_bit(R1BIO_FailFast, &r1_bio->state);

@@ -637,7 +635,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
                 sector_t first_bad;
                 int bad_sectors;
                 unsigned int pending;
-               bool nonrot;

                 rdev = conf->mirrors[disk].rdev;
                 if (r1_bio->bios[disk] == IO_BLOCKED
@@ -703,8 +700,6 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
                         /* At least two disks to choose from so failfast is OK */
                         set_bit(R1BIO_FailFast, &r1_bio->state);

-               nonrot = bdev_nonrot(rdev->bdev);
-               has_nonrot_disk |= nonrot;
                 pending = atomic_read(&rdev->nr_pending);
                 dist = abs(this_sector - conf->mirrors[disk].head_position);
                 if (choose_first) {
@@ -731,7 +726,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
                          * small, but not a big deal since when the second disk
                          * starts IO, the first disk is likely still busy.
                          */
-                       if (nonrot && opt_iosize > 0 &&
+                       if (test_bit(Nonrot, &rdev->flags) && opt_iosize > 0 &&
                             mirror->seq_start != MaxSector &&
                             mirror->next_seq_sect > opt_iosize &&
                             mirror->next_seq_sect - opt_iosize >=
@@ -763,7 +758,7 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
          * mixed ratation/non-rotational disks depending on workload.
          */
         if (best_disk == -1) {
-               if (has_nonrot_disk || min_pending == 0)
+               if (READ_ONCE(conf->nonrot_disks) || min_pending == 0)
                         best_disk = best_pending_disk;
                 else
                         best_disk = best_dist_disk;
@@ -1819,6 +1814,11 @@ static int raid1_add_disk(struct mddev *mddev, struct md_rdev *rdev)
                 WRITE_ONCE(p[conf->raid_disks].rdev, rdev);
         }

+       if (!err && bdev_nonrot(rdev->bdev)) {
+               set_bit(Nonrot, &rdev->flags);
+               WRITE_ONCE(conf->nonrot_disks, conf->nonrot_disks + 1);
+       }
+

Hi Kuai

I noticed raid1_run->setup_conf is used to add rdev to conf when
creating raid1. raid1_add_disk is only used for --add/--re-add after
creating array. So we need to add the same logic in setup_conf?

Yes, it's right. I'll add a helper raid1_add_conf(raid1_info, rdev) and
raid1_remove_conf(raid1_info, rdev) to do this, make sure all the places
to modify conf is covered.

Thanks,
Kuai


Regards
Xiao
         print_conf(conf);
         return err;
  }
@@ -1883,6 +1883,9 @@ static int raid1_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
         }
  abort:

+       if (test_and_clear_bit(Nonrot, &rdev->flags))
+               WRITE_ONCE(conf->nonrot_disks, conf->nonrot_disks - 1);
+
         print_conf(conf);
         return err;
  }
diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h
index 14d4211a123a..5300cbaa58a4 100644
--- a/drivers/md/raid1.h
+++ b/drivers/md/raid1.h
@@ -71,6 +71,7 @@ struct r1conf {
                                                  * allow for replacements.
                                                  */
         int                     raid_disks;
+       int                     nonrot_disks;

         spinlock_t              device_lock;

--
2.39.2


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