md/raid1: factor out the code to manage sequential IO

There is no functional change for now, make read_balance() cleaner and
prepare to fix problems and refactor the handler of sequential IO.

Co-developed-by: Paul Luse <paul.e.luse@linux.intel.com>
Signed-off-by: Paul Luse <paul.e.luse@linux.intel.com>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20240229095714.926789-11-yukuai1@huaweicloud.com

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index f6e75c123e5aef9450ae8d10ce003d738bf8cc40..17c2201d5d2b4177330472d9b3084de161f9500f 100644 (file)
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -705,6 +705,31 @@ static int choose_slow_rdev(struct r1conf *conf, struct r1bio *r1_bio,
        return bb_disk;
 }
 
+static bool is_sequential(struct r1conf *conf, int disk, struct r1bio *r1_bio)
+{
+       /* TODO: address issues with this check and concurrency. */
+       return conf->mirrors[disk].next_seq_sect == r1_bio->sector ||
+              conf->mirrors[disk].head_position == r1_bio->sector;
+}
+
+/*
+ * If buffered sequential IO size exceeds optimal iosize, check if there is idle
+ * disk. If yes, choose the idle disk.
+ */
+static bool should_choose_next(struct r1conf *conf, int disk)
+{
+       struct raid1_info *mirror = &conf->mirrors[disk];
+       int opt_iosize;
+
+       if (!test_bit(Nonrot, &mirror->rdev->flags))
+               return false;
+
+       opt_iosize = bdev_io_opt(mirror->rdev->bdev) >> 9;
+       return opt_iosize > 0 && mirror->seq_start != MaxSector &&
+              mirror->next_seq_sect > opt_iosize &&
+              mirror->next_seq_sect - opt_iosize >= mirror->seq_start;
+}
+
 /*
  * This routine returns the disk from which the requested read should
  * be done. There is a per-array 'next expected sequential IO' sector
@@ -768,43 +793,21 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
                pending = atomic_read(&rdev->nr_pending);
                dist = abs(this_sector - conf->mirrors[disk].head_position);
                /* Don't change to another disk for sequential reads */
-               if (conf->mirrors[disk].next_seq_sect == this_sector
-                   || dist == 0) {
-                       int opt_iosize = bdev_io_opt(rdev->bdev) >> 9;
-                       struct raid1_info *mirror = &conf->mirrors[disk];
-
-                       /*
-                        * If buffered sequential IO size exceeds optimal
-                        * iosize, check if there is idle disk. If yes, choose
-                        * the idle disk. read_balance could already choose an
-                        * idle disk before noticing it's a sequential IO in
-                        * this disk. This doesn't matter because this disk
-                        * will idle, next time it will be utilized after the
-                        * first disk has IO size exceeds optimal iosize. In
-                        * this way, iosize of the first disk will be optimal
-                        * iosize at least. iosize of the second disk might be
-                        * small, but not a big deal since when the second disk
-                        * starts IO, the first disk is likely still busy.
-                        */
-                       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 >=
-                           mirror->seq_start) {
-                               /*
-                                * Add 'pending' to avoid choosing this disk if
-                                * there is other idle disk.
-                                */
-                               pending++;
-                               /*
-                                * If there is no other idle disk, this disk
-                                * will be chosen.
-                                */
-                               sequential_disk = disk;
-                       } else {
+               if (is_sequential(conf, disk, r1_bio)) {
+                       if (!should_choose_next(conf, disk)) {
                                best_disk = disk;
                                break;
                        }
+                       /*
+                        * Add 'pending' to avoid choosing this disk if
+                        * there is other idle disk.
+                        */
+                       pending++;
+                       /*
+                        * If there is no other idle disk, this disk
+                        * will be chosen.
+                        */
+                       sequential_disk = disk;
                }
 
                if (min_pending > pending) {