Re: [PATCH 2/3] btrfs: volumes: Add btrfs_fs_devices::missing_list to collect missing devices

Anand Jain
2019-11-19T10:05:01Z

On 11/7/19 2:27 PM, Qu Wenruo wrote:
> This enables btrfs to iterate missing devices separately, without
> iterating all fs_devices.

IMO.
We don't need another list to maintain the missing device. We already
have good enough device lists.
The way its been implemented is
Allo_list is the only list from which we shall alloc the chunks.
Missing is a state of the device.
A device in the alloc list can be in the Missing state.

If there is missing_list that means the device in the missing list
is also possible candidate for the alloc that's messy.
Also its not typical to have a larger number of missing devices
to constitute its own list.

Thanks, Anand

> This provides the basis for later degraded chunk enhancement.
>
> The change includes:
> - Add missing devices to btrfs_fs_devices::missing_list
> This happens at add_missing_dev() and other locations where
> missing_devices get increased.
>
> - Remove missing devices from btrfs_fs_devices::missing_list
> This needs to cover all locations where missing_devices get decreased.
>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
> fs/btrfs/volumes.c | 27 +++++++++++++++++++++------
> fs/btrfs/volumes.h | 6 ++++++
> 2 files changed, 27 insertions(+), 6 deletions(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index eee5fc1d11f0..a462d8de5d2a 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -324,6 +324,7 @@ static struct btrfs_fs_devices *alloc_fs_devices(const u8 *fsid,
>
> INIT_LIST_HEAD(&fs_devs->devices);
> INIT_LIST_HEAD(&fs_devs->alloc_list);
> + INIT_LIST_HEAD(&fs_devs->missing_list);
> INIT_LIST_HEAD(&fs_devs->fs_list);
> if (fsid)
> memcpy(fs_devs->fsid, fsid, BTRFS_FSID_SIZE);
> @@ -1089,6 +1090,7 @@ static noinline struct btrfs_device *device_list_add(const char *path,
> if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) {
> fs_devices->missing_devices--;
> clear_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
> + list_del_init(&device->dev_alloc_list);
> }
> }
>
> @@ -1250,11 +1252,10 @@ static void btrfs_close_one_device(struct btrfs_device *device)
> if (device->bdev)
> fs_devices->open_devices--;
>
> + list_del_init(&device->dev_alloc_list);
> if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) &&
> - device->devid != BTRFS_DEV_REPLACE_DEVID) {
> - list_del_init(&device->dev_alloc_list);
> + device->devid != BTRFS_DEV_REPLACE_DEVID)
> fs_devices->rw_devices--;
> - }
>
> if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
> fs_devices->missing_devices--;
> @@ -2140,6 +2141,12 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
> device->fs_devices->rw_devices--;
> mutex_unlock(&fs_info->chunk_mutex);
> }
> + if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) {
> + mutex_lock(&fs_info->chunk_mutex);
> + list_del_init(&device->dev_alloc_list);
> + device->fs_devices->missing_devices--;
> + mutex_unlock(&fs_info->chunk_mutex);
> + }
>
> mutex_unlock(&uuid_mutex);
> ret = btrfs_shrink_device(device, 0);
> @@ -2184,9 +2191,6 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
> if (cur_devices != fs_devices)
> fs_devices->total_devices--;
>
> - if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
> - cur_devices->missing_devices--;
> -
> btrfs_assign_next_active_device(device, NULL);
>
> if (device->bdev) {
> @@ -2236,6 +2240,13 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
> device->fs_devices->rw_devices++;
> mutex_unlock(&fs_info->chunk_mutex);
> }
> + if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state)) {
> + mutex_lock(&fs_info->chunk_mutex);
> + list_add(&device->dev_alloc_list,
> + &fs_devices->missing_list);
> + device->fs_devices->missing_devices++;
> + mutex_unlock(&fs_info->chunk_mutex);
> + }
> goto out;
> }
>
> @@ -2438,6 +2449,7 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info)
> seed_devices->opened = 1;
> INIT_LIST_HEAD(&seed_devices->devices);
> INIT_LIST_HEAD(&seed_devices->alloc_list);
> + INIT_LIST_HEAD(&seed_devices->missing_list);
> mutex_init(&seed_devices->device_list_mutex);
>
> mutex_lock(&fs_devices->device_list_mutex);
> @@ -6640,6 +6652,7 @@ static struct btrfs_device *add_missing_dev(struct btrfs_fs_devices *fs_devices,
> fs_devices->num_devices++;
>
> set_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
> + list_add(&device->dev_alloc_list, &fs_devices->missing_list);
> fs_devices->missing_devices++;
>
> return device;
> @@ -6979,6 +6992,7 @@ static int read_one_dev(struct extent_buffer *leaf,
> */
> device->fs_devices->missing_devices++;
> set_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state);
> + list_add(&device->dev_alloc_list, &fs_devices->missing_list);
> }
>
> /* Move the device to its own fs_devices */
> @@ -6992,6 +7006,7 @@ static int read_one_dev(struct extent_buffer *leaf,
>
> device->fs_devices->missing_devices--;
> fs_devices->missing_devices++;
> + list_move(&device->dev_alloc_list, &fs_devices->missing_list);
>
> device->fs_devices = fs_devices;
> }
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index a7da1f3e3627..9cef4dc4b5be 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -253,6 +253,12 @@ struct btrfs_fs_devices {
> */
> struct list_head alloc_list;
>
> + /*
> + * Devices which can't be found. Projected by chunk_mutex.
> + * This acts as a fallback allocation list for certain degraded mount.
> + */
> + struct list_head missing_list;
> +
> struct btrfs_fs_devices *seed;
> int seeding;
>
>