btrfs: auto enable discard=async when possible

There's a request to automatically enable async discard for capable
devices. We can do that, the async mode is designed to wait for larger
freed extents and is not intrusive, with limits to iops, kbps or latency.

The status and tunables will be exported in /sys/fs/btrfs/FSID/discard .

The automatic selection is done if there's at least one discard capable
device in the filesystem (not capable devices are skipped). Mounting
with any other discard option will honor that option, notably mounting
with nodiscard will keep it disabled.

Link: https://lore.kernel.org/linux-btrfs/CAEg-Je_b1YtdsCR0zS5XZ_SbvJgN70ezwvRwLiCZgDGLbeMB=w@mail.gmail.com/
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 5adf76d89f9b31d1046b322ec56f3da395ea2462..3485f60efa330e6137235ba8e79b3477ffd34d17 100644 (file)
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1396,6 +1396,7 @@ enum {
        BTRFS_MOUNT_DISCARD_ASYNC               = (1UL << 28),
        BTRFS_MOUNT_IGNOREBADROOTS              = (1UL << 29),
        BTRFS_MOUNT_IGNOREDATACSUMS             = (1UL << 30),
+       BTRFS_MOUNT_NODISCARD                   = (1UL << 31),
 };
 
 #define BTRFS_DEFAULT_COMMIT_INTERVAL  (30)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 5705335c80c8b8b5f95c4d7147b9416a8ac4a3bb..cf59d8f14a056869613423d64cdb15fca6ca6c2e 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3746,6 +3746,20 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
                btrfs_set_and_info(fs_info, SSD, "enabling ssd optimizations");
        }
 
+       /*
+        * For devices supporting discard turn on discard=async automatically,
+        * unless it's already set or disabled. This could be turned off by
+        * nodiscard for the same mount.
+        */
+       if (!(btrfs_test_opt(fs_info, DISCARD_SYNC) ||
+             btrfs_test_opt(fs_info, DISCARD_ASYNC) ||
+             btrfs_test_opt(fs_info, NODISCARD)) &&
+           fs_info->fs_devices->discardable) {
+               btrfs_set_and_info(fs_info, DISCARD_ASYNC,
+                                  "auto enabling async discard");
+               btrfs_clear_opt(fs_info->mount_opt, NODISCARD);
+       }
+
        /*
         * Mount does not set all options immediately, we can do it now and do
         * not have to wait for transaction commit

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 3a33dd9847d9804b527cd7bc1e8f430efc0a5ba4..42e0d2fcc4073ae62008afcbab3769dc329bb935 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -918,12 +918,14 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
                                ret = -EINVAL;
                                goto out;
                        }
+                       btrfs_clear_opt(info->mount_opt, NODISCARD);
                        break;
                case Opt_nodiscard:
                        btrfs_clear_and_info(info, DISCARD_SYNC,
                                             "turning off discard");
                        btrfs_clear_and_info(info, DISCARD_ASYNC,
                                             "turning off async discard");
+                       btrfs_set_opt(info->mount_opt, NODISCARD);
                        break;
                case Opt_space_cache:
                case Opt_space_cache_version:

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 635f45f1a2ef80508f850ee593b8375786d1fc25..796e9f5ff8f84876c21fe5baf46705c7ea933641 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -641,6 +641,9 @@ static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices,
        if (!bdev_nonrot(bdev))
                fs_devices->rotating = true;
 
+       if (bdev_max_discard_sectors(bdev))
+               fs_devices->discardable = true;
+
        device->bdev = bdev;
        clear_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
        device->mode = flags;

diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 099def5613b875a3cdae1997f4cc34faef898919..a20ee7d5783155cbf93ea3ba0440b221bb7956da 100644 (file)
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -354,6 +354,8 @@ struct btrfs_fs_devices {
         * nonrot flag set
         */
        bool rotating;
+       /* Devices support TRIM/discard commands */
+       bool discardable;
 
        struct btrfs_fs_info *fs_info;
        /* sysfs kobjects */