[PATCH 1/2] btrfs: Fix lost-data-profile caused by auto removing bg

[PATCH 1/2] btrfs: Fix lost-data-profile caused by auto removing bg

[Zhao Lei]

Reproduce:
 (In integration-4.3 branch)

 TEST_DEV=(/dev/vdg /dev/vdh)
 TEST_DIR=/mnt/tmp

 umount "$TEST_DEV" >/dev/null
 mkfs.btrfs -f -d raid1 "${TEST_DEV[@]}"

 mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
 umount "$TEST_DEV"

 mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
 btrfs filesystem usage $TEST_DIR

We can see the data chunk changed from raid1 to single:
 # btrfs filesystem usage $TEST_DIR
 Data,single: Size:8.00MiB, Used:0.00B
    /dev/vdg        8.00MiB
 #

Reason:
 When a empty filesystem mount with -o nospace_cache, the last
 data blockgroup will be auto-removed in umount.

 Then if we mount it again, there is no data chunk in the
 filesystem, so the only available data profile is 0x0, result
 is all new chunks are created as single type.

Fix:
 Don't auto-delete last blockgroup for a raid type.

Test:
 Test by above script, and confirmed the logic by debug output.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
---
 fs/btrfs/extent-tree.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 79a5bd9..3505649 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -10012,7 +10012,8 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
 					       bg_list);
 		space_info = block_group->space_info;
 		list_del_init(&block_group->bg_list);
-		if (ret || btrfs_mixed_space_info(space_info)) {
+		if (ret || btrfs_mixed_space_info(space_info) ||
+		    block_group->list.next == block_group->list.prev) {
 			btrfs_put_block_group(block_group);
 			continue;
 		}
-- 
1.8.5.1

[PATCH 2/2] btrfs: Fix lost-data-profile caused by balance bg

[Zhao Lei]

Reproduce:
 (In integration-4.3 branch)

 TEST_DEV=(/dev/vdg /dev/vdh)
 TEST_DIR=/mnt/tmp

 umount "$TEST_DEV" >/dev/null
 mkfs.btrfs -f -d raid1 "${TEST_DEV[@]}"

 mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
 btrfs balance start -dusage=0 $TEST_DIR
 btrfs filesystem usage $TEST_DIR

 dd if=/dev/zero of="$TEST_DIR"/file count=100
 btrfs filesystem usage $TEST_DIR

Result:
 We can see "no data chunk" in first "btrfs filesystem usage":
 # btrfs filesystem usage $TEST_DIR
 Overall:
    ...
 Metadata,single: Size:8.00MiB, Used:0.00B
    /dev/vdg        8.00MiB
 Metadata,RAID1: Size:122.88MiB, Used:112.00KiB
    /dev/vdg      122.88MiB
    /dev/vdh      122.88MiB
 System,single: Size:4.00MiB, Used:0.00B
    /dev/vdg        4.00MiB
 System,RAID1: Size:8.00MiB, Used:16.00KiB
    /dev/vdg        8.00MiB
    /dev/vdh        8.00MiB
 Unallocated:
    /dev/vdg        1.06GiB
    /dev/vdh        1.07GiB

 And "data chunks changed from raid1 to single" in second
 "btrfs filesystem usage":
 # btrfs filesystem usage $TEST_DIR
 Overall:
    ...
 Data,single: Size:256.00MiB, Used:0.00B
    /dev/vdh      256.00MiB
 Metadata,single: Size:8.00MiB, Used:0.00B
    /dev/vdg        8.00MiB
 Metadata,RAID1: Size:122.88MiB, Used:112.00KiB
    /dev/vdg      122.88MiB
    /dev/vdh      122.88MiB
 System,single: Size:4.00MiB, Used:0.00B
    /dev/vdg        4.00MiB
 System,RAID1: Size:8.00MiB, Used:16.00KiB
    /dev/vdg        8.00MiB
    /dev/vdh        8.00MiB
 Unallocated:
    /dev/vdg        1.06GiB
    /dev/vdh      841.92MiB

Reason:
 btrfs balance delete last data chunk in case of no data in
 the filesystem, then we can see "no data chunk" by "fi usage"
 command.

 And when we do write operation to fs, the only available data
 profile is 0x0, result is all new chunks are allocated single type.

Fix:
 Allocate a data chunk explicitly in balance operation, to reserve
 at least one data chunk in the filesystem.

Test:
 Test by above script, and confirmed the logic by debug output.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
---
 fs/btrfs/volumes.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 6fc73586..3d5e41e 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3277,6 +3277,7 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info)
 	u64 limit_data = bctl->data.limit;
 	u64 limit_meta = bctl->meta.limit;
 	u64 limit_sys = bctl->sys.limit;
+	int chunk_reserved = 0;
 
 	/* step one make some room on all the devices */
 	devices = &fs_info->fs_devices->devices;
@@ -3387,6 +3388,24 @@ again:
 			goto loop;
 		}
 
+		if (!chunk_reserved) {
+			trans = btrfs_start_transaction(chunk_root, 0);
+			if (IS_ERR(trans)) {
+				mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+				ret = PTR_ERR(trans);
+				goto error;
+			}
+
+			ret = btrfs_force_chunk_alloc(trans, chunk_root, 1);
+			if (ret < 0) {
+				mutex_unlock(&fs_info->delete_unused_bgs_mutex);
+				goto error;
+			}
+
+			btrfs_end_transaction(trans, chunk_root);
+			chunk_reserved = 1;
+		}
+
 		ret = btrfs_relocate_chunk(chunk_root,
 					   found_key.offset);
 		mutex_unlock(&fs_info->delete_unused_bgs_mutex);
-- 
1.8.5.1

Re: [PATCH 2/2] btrfs: Fix lost-data-profile caused by balance bg

[Filipe Manana]

On Tue, Sep 29, 2015 at 2:51 PM, Zhao Lei <zhaolei@cn.fujitsu.com> wrote:
> Reproduce:
>  (In integration-4.3 branch)
>
>  TEST_DEV=(/dev/vdg /dev/vdh)
>  TEST_DIR=/mnt/tmp
>
>  umount "$TEST_DEV" >/dev/null
>  mkfs.btrfs -f -d raid1 "${TEST_DEV[@]}"
>
>  mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
>  btrfs balance start -dusage=0 $TEST_DIR
>  btrfs filesystem usage $TEST_DIR
>
>  dd if=/dev/zero of="$TEST_DIR"/file count=100
>  btrfs filesystem usage $TEST_DIR
>
> Result:
>  We can see "no data chunk" in first "btrfs filesystem usage":
>  # btrfs filesystem usage $TEST_DIR
>  Overall:
>     ...
>  Metadata,single: Size:8.00MiB, Used:0.00B
>     /dev/vdg        8.00MiB
>  Metadata,RAID1: Size:122.88MiB, Used:112.00KiB
>     /dev/vdg      122.88MiB
>     /dev/vdh      122.88MiB
>  System,single: Size:4.00MiB, Used:0.00B
>     /dev/vdg        4.00MiB
>  System,RAID1: Size:8.00MiB, Used:16.00KiB
>     /dev/vdg        8.00MiB
>     /dev/vdh        8.00MiB
>  Unallocated:
>     /dev/vdg        1.06GiB
>     /dev/vdh        1.07GiB
>
>  And "data chunks changed from raid1 to single" in second
>  "btrfs filesystem usage":
>  # btrfs filesystem usage $TEST_DIR
>  Overall:
>     ...
>  Data,single: Size:256.00MiB, Used:0.00B
>     /dev/vdh      256.00MiB
>  Metadata,single: Size:8.00MiB, Used:0.00B
>     /dev/vdg        8.00MiB
>  Metadata,RAID1: Size:122.88MiB, Used:112.00KiB
>     /dev/vdg      122.88MiB
>     /dev/vdh      122.88MiB
>  System,single: Size:4.00MiB, Used:0.00B
>     /dev/vdg        4.00MiB
>  System,RAID1: Size:8.00MiB, Used:16.00KiB
>     /dev/vdg        8.00MiB
>     /dev/vdh        8.00MiB
>  Unallocated:
>     /dev/vdg        1.06GiB
>     /dev/vdh      841.92MiB
>
> Reason:
>  btrfs balance delete last data chunk in case of no data in
>  the filesystem, then we can see "no data chunk" by "fi usage"
>  command.
>
>  And when we do write operation to fs, the only available data
>  profile is 0x0, result is all new chunks are allocated single type.
>
> Fix:
>  Allocate a data chunk explicitly in balance operation, to reserve
>  at least one data chunk in the filesystem.

Allocate a data chunk explicitly to ensure we don't lose the raid
profile for data.

>
> Test:
>  Test by above script, and confirmed the logic by debug output.
>
> Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
> ---
>  fs/btrfs/volumes.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 6fc73586..3d5e41e 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -3277,6 +3277,7 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info)
>         u64 limit_data = bctl->data.limit;
>         u64 limit_meta = bctl->meta.limit;
>         u64 limit_sys = bctl->sys.limit;
> +       int chunk_reserved = 0;
>
>         /* step one make some room on all the devices */
>         devices = &fs_info->fs_devices->devices;
> @@ -3387,6 +3388,24 @@ again:
>                         goto loop;
>                 }
>
> +               if (!chunk_reserved) {
> +                       trans = btrfs_start_transaction(chunk_root, 0);
> +                       if (IS_ERR(trans)) {
> +                               mutex_unlock(&fs_info->delete_unused_bgs_mutex);
> +                               ret = PTR_ERR(trans);
> +                               goto error;
> +                       }
> +
> +                       ret = btrfs_force_chunk_alloc(trans, chunk_root, 1);

Can we please use the symbol BTRFS_BLOCK_GROUP_DATA instead of 1?

> +                       if (ret < 0) {
> +                               mutex_unlock(&fs_info->delete_unused_bgs_mutex);
> +                               goto error;
> +                       }
> +
> +                       btrfs_end_transaction(trans, chunk_root);
> +                       chunk_reserved = 1;
> +               }

Can we do this logic only if the block group is a data one? I.e. no
point allocating a data block group if our balance only touches
metadata ones (due to some filter for e.g.).

Also, can't this be ineffective when the data block group we allocate
ends up with a key  in the chunk_root that is lower than the key we
found in the current iteration? I.e., key found in current iteration
has object id B, we allocate a new block group which gets a  key with
object id A, where A < B and the next iteration of our loop sees key
A, deletes the respective block group A if it's empty. In the end we
have no data block groups, assuming that before A there are no other
non-empty data block groups.
Your example works because there's no free space before the offset
where the chunk starts in the device.

thanks

> +
>                 ret = btrfs_relocate_chunk(chunk_root,
>                                            found_key.offset);
>                 mutex_unlock(&fs_info->delete_unused_bgs_mutex);
> --
> 1.8.5.1
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html



-- 
Filipe David Manana,

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."

RE: [PATCH 2/2] btrfs: Fix lost-data-profile caused by balance bg

[Zhao Lei]

Hi, Filipe Manana

Thanks for reviewing.

> -----Original Message-----
> From: Filipe Manana [mailto:fdmanana@gmail.com]
> Sent: Tuesday, September 29, 2015 11:48 PM
> To: Zhao Lei <zhaolei@cn.fujitsu.com>
> Cc: linux-btrfs@vger.kernel.org
> Subject: Re: [PATCH 2/2] btrfs: Fix lost-data-profile caused by balance bg
> 
> On Tue, Sep 29, 2015 at 2:51 PM, Zhao Lei <zhaolei@cn.fujitsu.com> wrote:
> > Reproduce:
> >  (In integration-4.3 branch)
> >
> >  TEST_DEV=(/dev/vdg /dev/vdh)
> >  TEST_DIR=/mnt/tmp
> >
> >  umount "$TEST_DEV" >/dev/null
> >  mkfs.btrfs -f -d raid1 "${TEST_DEV[@]}"
> >
> >  mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
> >  btrfs balance start -dusage=0 $TEST_DIR  btrfs filesystem usage
> > $TEST_DIR
> >
> >  dd if=/dev/zero of="$TEST_DIR"/file count=100  btrfs filesystem usage
> > $TEST_DIR
> >
> > Result:
> >  We can see "no data chunk" in first "btrfs filesystem usage":
> >  # btrfs filesystem usage $TEST_DIR
> >  Overall:
> >     ...
> >  Metadata,single: Size:8.00MiB, Used:0.00B
> >     /dev/vdg        8.00MiB
> >  Metadata,RAID1: Size:122.88MiB, Used:112.00KiB
> >     /dev/vdg      122.88MiB
> >     /dev/vdh      122.88MiB
> >  System,single: Size:4.00MiB, Used:0.00B
> >     /dev/vdg        4.00MiB
> >  System,RAID1: Size:8.00MiB, Used:16.00KiB
> >     /dev/vdg        8.00MiB
> >     /dev/vdh        8.00MiB
> >  Unallocated:
> >     /dev/vdg        1.06GiB
> >     /dev/vdh        1.07GiB
> >
> >  And "data chunks changed from raid1 to single" in second  "btrfs
> > filesystem usage":
> >  # btrfs filesystem usage $TEST_DIR
> >  Overall:
> >     ...
> >  Data,single: Size:256.00MiB, Used:0.00B
> >     /dev/vdh      256.00MiB
> >  Metadata,single: Size:8.00MiB, Used:0.00B
> >     /dev/vdg        8.00MiB
> >  Metadata,RAID1: Size:122.88MiB, Used:112.00KiB
> >     /dev/vdg      122.88MiB
> >     /dev/vdh      122.88MiB
> >  System,single: Size:4.00MiB, Used:0.00B
> >     /dev/vdg        4.00MiB
> >  System,RAID1: Size:8.00MiB, Used:16.00KiB
> >     /dev/vdg        8.00MiB
> >     /dev/vdh        8.00MiB
> >  Unallocated:
> >     /dev/vdg        1.06GiB
> >     /dev/vdh      841.92MiB
> >
> > Reason:
> >  btrfs balance delete last data chunk in case of no data in  the
> > filesystem, then we can see "no data chunk" by "fi usage"
> >  command.
> >
> >  And when we do write operation to fs, the only available data
> > profile is 0x0, result is all new chunks are allocated single type.
> >
> > Fix:
> >  Allocate a data chunk explicitly in balance operation, to reserve  at
> > least one data chunk in the filesystem.
> 
> Allocate a data chunk explicitly to ensure we don't lose the raid profile for data.
> 

Thanks, will change in v2.

> >
> > Test:
> >  Test by above script, and confirmed the logic by debug output.
> >
> > Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
> > ---
> >  fs/btrfs/volumes.c | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)
> >
> > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index
> > 6fc73586..3d5e41e 100644
> > --- a/fs/btrfs/volumes.c
> > +++ b/fs/btrfs/volumes.c
> > @@ -3277,6 +3277,7 @@ static int __btrfs_balance(struct btrfs_fs_info
> *fs_info)
> >         u64 limit_data = bctl->data.limit;
> >         u64 limit_meta = bctl->meta.limit;
> >         u64 limit_sys = bctl->sys.limit;
> > +       int chunk_reserved = 0;
> >
> >         /* step one make some room on all the devices */
> >         devices = &fs_info->fs_devices->devices; @@ -3387,6 +3388,24
> > @@ again:
> >                         goto loop;
> >                 }
> >
> > +               if (!chunk_reserved) {
> > +                       trans = btrfs_start_transaction(chunk_root, 0);
> > +                       if (IS_ERR(trans)) {
> > +
> mutex_unlock(&fs_info->delete_unused_bgs_mutex);
> > +                               ret = PTR_ERR(trans);
> > +                               goto error;
> > +                       }
> > +
> > +                       ret = btrfs_force_chunk_alloc(trans,
> > + chunk_root, 1);
> 
> Can we please use the symbol BTRFS_BLOCK_GROUP_DATA instead of 1?
> 
Thanks, will change in v2.


> > +                       if (ret < 0) {
> > +
> mutex_unlock(&fs_info->delete_unused_bgs_mutex);
> > +                               goto error;
> > +                       }
> > +
> > +                       btrfs_end_transaction(trans, chunk_root);
> > +                       chunk_reserved = 1;
> > +               }
> 
> Can we do this logic only if the block group is a data one? I.e. no point allocating
> a data block group if our balance only touches metadata ones (due to some
> filter for e.g.).
> 
Thanks for point out it, will change in v2.

> Also, can't this be ineffective when the data block group we allocate ends up
> with a key  in the chunk_root that is lower than the key we found in the
> current iteration? I.e., key found in current iteration has object id B, we
> allocate a new block group which gets a  key with object id A, where A < B and
> the next iteration of our loop sees key A, deletes the respective block group A if
> it's empty. In the end we have no data block groups, assuming that before A
> there are no other non-empty data block groups.
> Your example works because there's no free space before the offset where the
> chunk starts in the device.
> 
New chunk will always use increased logic address, even if there are "hole" before,
so A's logic address will always >B.
And current code of balance also use this feature to avoid balance new-created
chunks(which was created by balance operation itself).

Thanks
Zhaolei

> thanks
> 
> > +
> >                 ret = btrfs_relocate_chunk(chunk_root,
> >                                            found_key.offset);
> >                 mutex_unlock(&fs_info->delete_unused_bgs_mutex);
> > --
> > 1.8.5.1
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-btrfs"
> > in the body of a message to majordomo@vger.kernel.org More majordomo
> > info at  http://vger.kernel.org/majordomo-info.html
> 
> 
> 
> --
> Filipe David Manana,
> 
> "Reasonable men adapt themselves to the world.
>  Unreasonable men adapt the world to themselves.
>  That's why all progress depends on unreasonable men."

Re: [PATCH 2/2] btrfs: Fix lost-data-profile caused by balance bg

[Filipe Manana]

On Wed, Sep 30, 2015 at 5:20 AM, Zhao Lei <zhaolei@cn.fujitsu.com> wrote:
> Hi, Filipe Manana
>
> Thanks for reviewing.
>
>> -----Original Message-----
>> From: Filipe Manana [mailto:fdmanana@gmail.com]
>> Sent: Tuesday, September 29, 2015 11:48 PM
>> To: Zhao Lei <zhaolei@cn.fujitsu.com>
>> Cc: linux-btrfs@vger.kernel.org
>> Subject: Re: [PATCH 2/2] btrfs: Fix lost-data-profile caused by balance bg
>>
>> On Tue, Sep 29, 2015 at 2:51 PM, Zhao Lei <zhaolei@cn.fujitsu.com> wrote:
>> > Reproduce:
>> >  (In integration-4.3 branch)
>> >
>> >  TEST_DEV=(/dev/vdg /dev/vdh)
>> >  TEST_DIR=/mnt/tmp
>> >
>> >  umount "$TEST_DEV" >/dev/null
>> >  mkfs.btrfs -f -d raid1 "${TEST_DEV[@]}"
>> >
>> >  mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
>> >  btrfs balance start -dusage=0 $TEST_DIR  btrfs filesystem usage
>> > $TEST_DIR
>> >
>> >  dd if=/dev/zero of="$TEST_DIR"/file count=100  btrfs filesystem usage
>> > $TEST_DIR
>> >
>> > Result:
>> >  We can see "no data chunk" in first "btrfs filesystem usage":
>> >  # btrfs filesystem usage $TEST_DIR
>> >  Overall:
>> >     ...
>> >  Metadata,single: Size:8.00MiB, Used:0.00B
>> >     /dev/vdg        8.00MiB
>> >  Metadata,RAID1: Size:122.88MiB, Used:112.00KiB
>> >     /dev/vdg      122.88MiB
>> >     /dev/vdh      122.88MiB
>> >  System,single: Size:4.00MiB, Used:0.00B
>> >     /dev/vdg        4.00MiB
>> >  System,RAID1: Size:8.00MiB, Used:16.00KiB
>> >     /dev/vdg        8.00MiB
>> >     /dev/vdh        8.00MiB
>> >  Unallocated:
>> >     /dev/vdg        1.06GiB
>> >     /dev/vdh        1.07GiB
>> >
>> >  And "data chunks changed from raid1 to single" in second  "btrfs
>> > filesystem usage":
>> >  # btrfs filesystem usage $TEST_DIR
>> >  Overall:
>> >     ...
>> >  Data,single: Size:256.00MiB, Used:0.00B
>> >     /dev/vdh      256.00MiB
>> >  Metadata,single: Size:8.00MiB, Used:0.00B
>> >     /dev/vdg        8.00MiB
>> >  Metadata,RAID1: Size:122.88MiB, Used:112.00KiB
>> >     /dev/vdg      122.88MiB
>> >     /dev/vdh      122.88MiB
>> >  System,single: Size:4.00MiB, Used:0.00B
>> >     /dev/vdg        4.00MiB
>> >  System,RAID1: Size:8.00MiB, Used:16.00KiB
>> >     /dev/vdg        8.00MiB
>> >     /dev/vdh        8.00MiB
>> >  Unallocated:
>> >     /dev/vdg        1.06GiB
>> >     /dev/vdh      841.92MiB
>> >
>> > Reason:
>> >  btrfs balance delete last data chunk in case of no data in  the
>> > filesystem, then we can see "no data chunk" by "fi usage"
>> >  command.
>> >
>> >  And when we do write operation to fs, the only available data
>> > profile is 0x0, result is all new chunks are allocated single type.
>> >
>> > Fix:
>> >  Allocate a data chunk explicitly in balance operation, to reserve  at
>> > least one data chunk in the filesystem.
>>
>> Allocate a data chunk explicitly to ensure we don't lose the raid profile for data.
>>
>
> Thanks, will change in v2.
>
>> >
>> > Test:
>> >  Test by above script, and confirmed the logic by debug output.
>> >
>> > Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
>> > ---
>> >  fs/btrfs/volumes.c | 19 +++++++++++++++++++
>> >  1 file changed, 19 insertions(+)
>> >
>> > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index
>> > 6fc73586..3d5e41e 100644
>> > --- a/fs/btrfs/volumes.c
>> > +++ b/fs/btrfs/volumes.c
>> > @@ -3277,6 +3277,7 @@ static int __btrfs_balance(struct btrfs_fs_info
>> *fs_info)
>> >         u64 limit_data = bctl->data.limit;
>> >         u64 limit_meta = bctl->meta.limit;
>> >         u64 limit_sys = bctl->sys.limit;
>> > +       int chunk_reserved = 0;
>> >
>> >         /* step one make some room on all the devices */
>> >         devices = &fs_info->fs_devices->devices; @@ -3387,6 +3388,24
>> > @@ again:
>> >                         goto loop;
>> >                 }
>> >
>> > +               if (!chunk_reserved) {
>> > +                       trans = btrfs_start_transaction(chunk_root, 0);
>> > +                       if (IS_ERR(trans)) {
>> > +
>> mutex_unlock(&fs_info->delete_unused_bgs_mutex);
>> > +                               ret = PTR_ERR(trans);
>> > +                               goto error;
>> > +                       }
>> > +
>> > +                       ret = btrfs_force_chunk_alloc(trans,
>> > + chunk_root, 1);
>>
>> Can we please use the symbol BTRFS_BLOCK_GROUP_DATA instead of 1?
>>
> Thanks, will change in v2.
>
>
>> > +                       if (ret < 0) {
>> > +
>> mutex_unlock(&fs_info->delete_unused_bgs_mutex);
>> > +                               goto error;
>> > +                       }
>> > +
>> > +                       btrfs_end_transaction(trans, chunk_root);
>> > +                       chunk_reserved = 1;
>> > +               }
>>
>> Can we do this logic only if the block group is a data one? I.e. no point allocating
>> a data block group if our balance only touches metadata ones (due to some
>> filter for e.g.).
>>
> Thanks for point out it, will change in v2.

I find it somewhat awkward that we always allocate a new data block
group no matter what. Some balance operations that used to succeed in
the past may now fail with -ENOSPC for example...

How about making this simpler and not so special for data block
groups, like the following (compile tested only):

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 644e070..067b1eb 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2774,6 +2774,8 @@ static int btrfs_relocate_chunk(struct
btrfs_root *root, u64 chunk_offset)
        struct btrfs_root *extent_root;
        struct btrfs_trans_handle *trans;
        int ret;
+       struct btrfs_block_group_cache *bg;
+       bool remove = true;

        root = root->fs_info->chunk_root;
        extent_root = root->fs_info->extent_root;
@@ -2803,6 +2805,23 @@ static int btrfs_relocate_chunk(struct
btrfs_root *root, u64 chunk_offset)
        if (ret)
                return ret;

+       bg = btrfs_lookup_block_group(root->fs_info, chunk_offset);
+       ASSERT(bg);
+       down_read(&bg->space_info->groups_sem);
+       /*
+        * Do not remove the last block group of a kind to prevent losing
+        * raid profile information for future chunk allocations.
+        */
+       if (bg->list.next == bg->list.prev)
+               remove = false;
+       up_read(&bg->space_info->groups_sem);
+       if (!remove)
+               btrfs_dec_block_group_ro(extent_root, bg);
+       btrfs_put_block_group(bg);
+
+       if (!remove)
+               return 0;
+
        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);

(also at https://friendpaste.com/5IeAIIzBv3oKhureKfvjwm)

thanks


>
>> Also, can't this be ineffective when the data block group we allocate ends up
>> with a key  in the chunk_root that is lower than the key we found in the
>> current iteration? I.e., key found in current iteration has object id B, we
>> allocate a new block group which gets a  key with object id A, where A < B and
>> the next iteration of our loop sees key A, deletes the respective block group A if
>> it's empty. In the end we have no data block groups, assuming that before A
>> there are no other non-empty data block groups.
>> Your example works because there's no free space before the offset where the
>> chunk starts in the device.
>>
> New chunk will always use increased logic address, even if there are "hole" before,
> so A's logic address will always >B.
> And current code of balance also use this feature to avoid balance new-created
> chunks(which was created by balance operation itself).
>
> Thanks
> Zhaolei
>
>> thanks
>>
>> > +
>> >                 ret = btrfs_relocate_chunk(chunk_root,
>> >                                            found_key.offset);
>> >                 mutex_unlock(&fs_info->delete_unused_bgs_mutex);
>> > --
>> > 1.8.5.1
>> >
>> > --
>> > To unsubscribe from this list: send the line "unsubscribe linux-btrfs"
>> > in the body of a message to majordomo@vger.kernel.org More majordomo
>> > info at  http://vger.kernel.org/majordomo-info.html
>>
>>
>>
>> --
>> Filipe David Manana,
>>
>> "Reasonable men adapt themselves to the world.
>>  Unreasonable men adapt the world to themselves.
>>  That's why all progress depends on unreasonable men."
>



-- 
Filipe David Manana,

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."

RE: [PATCH 2/2] btrfs: Fix lost-data-profile caused by balance bg

[Zhao Lei]

Hi, Filipe Manana

> -----Original Message-----
> From: Filipe Manana [mailto:fdmanana@gmail.com]
> Sent: Wednesday, September 30, 2015 3:41 PM
> To: Zhao Lei <zhaolei@cn.fujitsu.com>
> Cc: linux-btrfs@vger.kernel.org
> Subject: Re: [PATCH 2/2] btrfs: Fix lost-data-profile caused by balance bg
> 
> On Wed, Sep 30, 2015 at 5:20 AM, Zhao Lei <zhaolei@cn.fujitsu.com> wrote:
> > Hi, Filipe Manana
> >
> > Thanks for reviewing.
> >
> >> -----Original Message-----
> >> From: Filipe Manana [mailto:fdmanana@gmail.com]
> >> Sent: Tuesday, September 29, 2015 11:48 PM
> >> To: Zhao Lei <zhaolei@cn.fujitsu.com>
> >> Cc: linux-btrfs@vger.kernel.org
> >> Subject: Re: [PATCH 2/2] btrfs: Fix lost-data-profile caused by
> >> balance bg
> >>
> >> On Tue, Sep 29, 2015 at 2:51 PM, Zhao Lei <zhaolei@cn.fujitsu.com> wrote:
> >> > Reproduce:
> >> >  (In integration-4.3 branch)
> >> >
> >> >  TEST_DEV=(/dev/vdg /dev/vdh)
> >> >  TEST_DIR=/mnt/tmp
> >> >
> >> >  umount "$TEST_DEV" >/dev/null
> >> >  mkfs.btrfs -f -d raid1 "${TEST_DEV[@]}"
> >> >
> >> >  mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
> >> >  btrfs balance start -dusage=0 $TEST_DIR  btrfs filesystem usage
> >> > $TEST_DIR
> >> >
> >> >  dd if=/dev/zero of="$TEST_DIR"/file count=100  btrfs filesystem
> >> > usage $TEST_DIR
> >> >
> >> > Result:
> >> >  We can see "no data chunk" in first "btrfs filesystem usage":
> >> >  # btrfs filesystem usage $TEST_DIR
> >> >  Overall:
> >> >     ...
> >> >  Metadata,single: Size:8.00MiB, Used:0.00B
> >> >     /dev/vdg        8.00MiB
> >> >  Metadata,RAID1: Size:122.88MiB, Used:112.00KiB
> >> >     /dev/vdg      122.88MiB
> >> >     /dev/vdh      122.88MiB
> >> >  System,single: Size:4.00MiB, Used:0.00B
> >> >     /dev/vdg        4.00MiB
> >> >  System,RAID1: Size:8.00MiB, Used:16.00KiB
> >> >     /dev/vdg        8.00MiB
> >> >     /dev/vdh        8.00MiB
> >> >  Unallocated:
> >> >     /dev/vdg        1.06GiB
> >> >     /dev/vdh        1.07GiB
> >> >
> >> >  And "data chunks changed from raid1 to single" in second  "btrfs
> >> > filesystem usage":
> >> >  # btrfs filesystem usage $TEST_DIR
> >> >  Overall:
> >> >     ...
> >> >  Data,single: Size:256.00MiB, Used:0.00B
> >> >     /dev/vdh      256.00MiB
> >> >  Metadata,single: Size:8.00MiB, Used:0.00B
> >> >     /dev/vdg        8.00MiB
> >> >  Metadata,RAID1: Size:122.88MiB, Used:112.00KiB
> >> >     /dev/vdg      122.88MiB
> >> >     /dev/vdh      122.88MiB
> >> >  System,single: Size:4.00MiB, Used:0.00B
> >> >     /dev/vdg        4.00MiB
> >> >  System,RAID1: Size:8.00MiB, Used:16.00KiB
> >> >     /dev/vdg        8.00MiB
> >> >     /dev/vdh        8.00MiB
> >> >  Unallocated:
> >> >     /dev/vdg        1.06GiB
> >> >     /dev/vdh      841.92MiB
> >> >
> >> > Reason:
> >> >  btrfs balance delete last data chunk in case of no data in  the
> >> > filesystem, then we can see "no data chunk" by "fi usage"
> >> >  command.
> >> >
> >> >  And when we do write operation to fs, the only available data
> >> > profile is 0x0, result is all new chunks are allocated single type.
> >> >
> >> > Fix:
> >> >  Allocate a data chunk explicitly in balance operation, to reserve
> >> > at least one data chunk in the filesystem.
> >>
> >> Allocate a data chunk explicitly to ensure we don't lose the raid profile for
> data.
> >>
> >
> > Thanks, will change in v2.
> >
> >> >
> >> > Test:
> >> >  Test by above script, and confirmed the logic by debug output.
> >> >
> >> > Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
> >> > ---
> >> >  fs/btrfs/volumes.c | 19 +++++++++++++++++++
> >> >  1 file changed, 19 insertions(+)
> >> >
> >> > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index
> >> > 6fc73586..3d5e41e 100644
> >> > --- a/fs/btrfs/volumes.c
> >> > +++ b/fs/btrfs/volumes.c
> >> > @@ -3277,6 +3277,7 @@ static int __btrfs_balance(struct
> >> > btrfs_fs_info
> >> *fs_info)
> >> >         u64 limit_data = bctl->data.limit;
> >> >         u64 limit_meta = bctl->meta.limit;
> >> >         u64 limit_sys = bctl->sys.limit;
> >> > +       int chunk_reserved = 0;
> >> >
> >> >         /* step one make some room on all the devices */
> >> >         devices = &fs_info->fs_devices->devices; @@ -3387,6
> >> > +3388,24 @@ again:
> >> >                         goto loop;
> >> >                 }
> >> >
> >> > +               if (!chunk_reserved) {
> >> > +                       trans = btrfs_start_transaction(chunk_root,
> 0);
> >> > +                       if (IS_ERR(trans)) {
> >> > +
> >> mutex_unlock(&fs_info->delete_unused_bgs_mutex);
> >> > +                               ret = PTR_ERR(trans);
> >> > +                               goto error;
> >> > +                       }
> >> > +
> >> > +                       ret = btrfs_force_chunk_alloc(trans,
> >> > + chunk_root, 1);
> >>
> >> Can we please use the symbol BTRFS_BLOCK_GROUP_DATA instead of 1?
> >>
> > Thanks, will change in v2.
> >
> >
> >> > +                       if (ret < 0) {
> >> > +
> >> mutex_unlock(&fs_info->delete_unused_bgs_mutex);
> >> > +                               goto error;
> >> > +                       }
> >> > +
> >> > +                       btrfs_end_transaction(trans, chunk_root);
> >> > +                       chunk_reserved = 1;
> >> > +               }
> >>
> >> Can we do this logic only if the block group is a data one? I.e. no
> >> point allocating a data block group if our balance only touches
> >> metadata ones (due to some filter for e.g.).
> >>
> > Thanks for point out it, will change in v2.
> 
> I find it somewhat awkward that we always allocate a new data block group no
> matter what. Some balance operations that used to succeed in the past may
> now fail with -ENOSPC for example...
> 
> How about making this simpler and not so special for data block groups, like the
> following (compile tested only):
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 644e070..067b1eb
> 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -2774,6 +2774,8 @@ static int btrfs_relocate_chunk(struct btrfs_root
> *root, u64 chunk_offset)
>         struct btrfs_root *extent_root;
>         struct btrfs_trans_handle *trans;
>         int ret;
> +       struct btrfs_block_group_cache *bg;
> +       bool remove = true;
> 
>         root = root->fs_info->chunk_root;
>         extent_root = root->fs_info->extent_root; @@ -2803,6 +2805,23
> @@ static int btrfs_relocate_chunk(struct btrfs_root *root, u64 chunk_offset)
>         if (ret)
>                 return ret;
> 
> +       bg = btrfs_lookup_block_group(root->fs_info, chunk_offset);
> +       ASSERT(bg);
> +       down_read(&bg->space_info->groups_sem);
> +       /*
> +        * Do not remove the last block group of a kind to prevent losing
> +        * raid profile information for future chunk allocations.
> +        */
> +       if (bg->list.next == bg->list.prev)
> +               remove = false;
> +       up_read(&bg->space_info->groups_sem);
> +       if (!remove)
> +               btrfs_dec_block_group_ro(extent_root, bg);
> +       btrfs_put_block_group(bg);
> +
> +       if (!remove)
> +               return 0;
> +
>         trans = btrfs_start_transaction(root, 0);
>         if (IS_ERR(trans)) {
>                 ret = PTR_ERR(trans);
> 

Thanks for your detailed review!

Reason of creating new bg is:
Balance operation may be used to change raid-profile of the filesystem.
If we want to change filesystem form raid1 to raid5, we need:
1: delete all raid1 bgs
2: move all data to raid5 bg if data exist in filesystem
3: reserve only one blank raid5 bg if no data in filesystem

If we use similar operation as patch 1/2(not delete lattest blockgroup),
we'll have following problem:
1: the old raid1 blockgroups are not all-deleted
2: if no data in filesystem, the profile will not changed from raid1 to raid5.

I understand your worry of "NO_SPACE" when create additional bg,
and I also considered it in making patch, but I choose to use this way because:
1: balance operation had check free space before operation
  (In front of __btrfs_balance)
2: for filesystem with data, we have to create target-chunk in balance operation,
  this patch only make "creating-chunk" earlier, and the created chunk will be used
  to save data in balance operation, and reduce one chunk-allocate in balance operation.
3: for a blank filesystem, it is necessary to create a blank chunk with of target raid profile.
  the old code hadn't create it, and this patch created. It is right operation even if
  cause no-space. Actually, create a chunk in empty filesystem rarely cause no-space,
  plus we have free-space check in 1.
4: 1~3 ensure this patch rarely cause additional no-space problem in logic.
  And if it really caused additional no-space(if out of my consideration),
  We can change code of 1 to avoid it.

Thanks
Zhaolei

> (also at https://friendpaste.com/5IeAIIzBv3oKhureKfvjwm)
> 
> thanks
> 
> 
> >
> >> Also, can't this be ineffective when the data block group we allocate
> >> ends up with a key  in the chunk_root that is lower than the key we
> >> found in the current iteration? I.e., key found in current iteration
> >> has object id B, we allocate a new block group which gets a  key with
> >> object id A, where A < B and the next iteration of our loop sees key
> >> A, deletes the respective block group A if it's empty. In the end we
> >> have no data block groups, assuming that before A there are no other
> non-empty data block groups.
> >> Your example works because there's no free space before the offset
> >> where the chunk starts in the device.
> >>
> > New chunk will always use increased logic address, even if there are
> > "hole" before, so A's logic address will always >B.
> > And current code of balance also use this feature to avoid balance
> > new-created chunks(which was created by balance operation itself).
> >
> > Thanks
> > Zhaolei
> >
> >> thanks
> >>
> >> > +
> >> >                 ret = btrfs_relocate_chunk(chunk_root,
> >> >                                            found_key.offset);
> >> >                 mutex_unlock(&fs_info->delete_unused_bgs_mutex);
> >> > --
> >> > 1.8.5.1
> >> >
> >> > --
> >> > To unsubscribe from this list: send the line "unsubscribe linux-btrfs"
> >> > in the body of a message to majordomo@vger.kernel.org More
> >> > majordomo info at  http://vger.kernel.org/majordomo-info.html
> >>
> >>
> >>
> >> --
> >> Filipe David Manana,
> >>
> >> "Reasonable men adapt themselves to the world.
> >>  Unreasonable men adapt the world to themselves.
> >>  That's why all progress depends on unreasonable men."
> >
> 
> 
> 
> --
> Filipe David Manana,
> 
> "Reasonable men adapt themselves to the world.
>  Unreasonable men adapt the world to themselves.
>  That's why all progress depends on unreasonable men."

Re: [PATCH 2/2] btrfs: Fix lost-data-profile caused by balance bg

[Filipe Manana]

On Wed, Sep 30, 2015 at 9:26 AM, Zhao Lei <zhaolei@cn.fujitsu.com> wrote:
> Hi, Filipe Manana
>
>> -----Original Message-----
>> From: Filipe Manana [mailto:fdmanana@gmail.com]
>> Sent: Wednesday, September 30, 2015 3:41 PM
>> To: Zhao Lei <zhaolei@cn.fujitsu.com>
>> Cc: linux-btrfs@vger.kernel.org
>> Subject: Re: [PATCH 2/2] btrfs: Fix lost-data-profile caused by balance bg
>>
>> On Wed, Sep 30, 2015 at 5:20 AM, Zhao Lei <zhaolei@cn.fujitsu.com> wrote:
>> > Hi, Filipe Manana
>> >
>> > Thanks for reviewing.
>> >
>> >> -----Original Message-----
>> >> From: Filipe Manana [mailto:fdmanana@gmail.com]
>> >> Sent: Tuesday, September 29, 2015 11:48 PM
>> >> To: Zhao Lei <zhaolei@cn.fujitsu.com>
>> >> Cc: linux-btrfs@vger.kernel.org
>> >> Subject: Re: [PATCH 2/2] btrfs: Fix lost-data-profile caused by
>> >> balance bg
>> >>
>> >> On Tue, Sep 29, 2015 at 2:51 PM, Zhao Lei <zhaolei@cn.fujitsu.com> wrote:
>> >> > Reproduce:
>> >> >  (In integration-4.3 branch)
>> >> >
>> >> >  TEST_DEV=(/dev/vdg /dev/vdh)
>> >> >  TEST_DIR=/mnt/tmp
>> >> >
>> >> >  umount "$TEST_DEV" >/dev/null
>> >> >  mkfs.btrfs -f -d raid1 "${TEST_DEV[@]}"
>> >> >
>> >> >  mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
>> >> >  btrfs balance start -dusage=0 $TEST_DIR  btrfs filesystem usage
>> >> > $TEST_DIR
>> >> >
>> >> >  dd if=/dev/zero of="$TEST_DIR"/file count=100  btrfs filesystem
>> >> > usage $TEST_DIR
>> >> >
>> >> > Result:
>> >> >  We can see "no data chunk" in first "btrfs filesystem usage":
>> >> >  # btrfs filesystem usage $TEST_DIR
>> >> >  Overall:
>> >> >     ...
>> >> >  Metadata,single: Size:8.00MiB, Used:0.00B
>> >> >     /dev/vdg        8.00MiB
>> >> >  Metadata,RAID1: Size:122.88MiB, Used:112.00KiB
>> >> >     /dev/vdg      122.88MiB
>> >> >     /dev/vdh      122.88MiB
>> >> >  System,single: Size:4.00MiB, Used:0.00B
>> >> >     /dev/vdg        4.00MiB
>> >> >  System,RAID1: Size:8.00MiB, Used:16.00KiB
>> >> >     /dev/vdg        8.00MiB
>> >> >     /dev/vdh        8.00MiB
>> >> >  Unallocated:
>> >> >     /dev/vdg        1.06GiB
>> >> >     /dev/vdh        1.07GiB
>> >> >
>> >> >  And "data chunks changed from raid1 to single" in second  "btrfs
>> >> > filesystem usage":
>> >> >  # btrfs filesystem usage $TEST_DIR
>> >> >  Overall:
>> >> >     ...
>> >> >  Data,single: Size:256.00MiB, Used:0.00B
>> >> >     /dev/vdh      256.00MiB
>> >> >  Metadata,single: Size:8.00MiB, Used:0.00B
>> >> >     /dev/vdg        8.00MiB
>> >> >  Metadata,RAID1: Size:122.88MiB, Used:112.00KiB
>> >> >     /dev/vdg      122.88MiB
>> >> >     /dev/vdh      122.88MiB
>> >> >  System,single: Size:4.00MiB, Used:0.00B
>> >> >     /dev/vdg        4.00MiB
>> >> >  System,RAID1: Size:8.00MiB, Used:16.00KiB
>> >> >     /dev/vdg        8.00MiB
>> >> >     /dev/vdh        8.00MiB
>> >> >  Unallocated:
>> >> >     /dev/vdg        1.06GiB
>> >> >     /dev/vdh      841.92MiB
>> >> >
>> >> > Reason:
>> >> >  btrfs balance delete last data chunk in case of no data in  the
>> >> > filesystem, then we can see "no data chunk" by "fi usage"
>> >> >  command.
>> >> >
>> >> >  And when we do write operation to fs, the only available data
>> >> > profile is 0x0, result is all new chunks are allocated single type.
>> >> >
>> >> > Fix:
>> >> >  Allocate a data chunk explicitly in balance operation, to reserve
>> >> > at least one data chunk in the filesystem.
>> >>
>> >> Allocate a data chunk explicitly to ensure we don't lose the raid profile for
>> data.
>> >>
>> >
>> > Thanks, will change in v2.
>> >
>> >> >
>> >> > Test:
>> >> >  Test by above script, and confirmed the logic by debug output.
>> >> >
>> >> > Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
>> >> > ---
>> >> >  fs/btrfs/volumes.c | 19 +++++++++++++++++++
>> >> >  1 file changed, 19 insertions(+)
>> >> >
>> >> > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index
>> >> > 6fc73586..3d5e41e 100644
>> >> > --- a/fs/btrfs/volumes.c
>> >> > +++ b/fs/btrfs/volumes.c
>> >> > @@ -3277,6 +3277,7 @@ static int __btrfs_balance(struct
>> >> > btrfs_fs_info
>> >> *fs_info)
>> >> >         u64 limit_data = bctl->data.limit;
>> >> >         u64 limit_meta = bctl->meta.limit;
>> >> >         u64 limit_sys = bctl->sys.limit;
>> >> > +       int chunk_reserved = 0;
>> >> >
>> >> >         /* step one make some room on all the devices */
>> >> >         devices = &fs_info->fs_devices->devices; @@ -3387,6
>> >> > +3388,24 @@ again:
>> >> >                         goto loop;
>> >> >                 }
>> >> >
>> >> > +               if (!chunk_reserved) {
>> >> > +                       trans = btrfs_start_transaction(chunk_root,
>> 0);
>> >> > +                       if (IS_ERR(trans)) {
>> >> > +
>> >> mutex_unlock(&fs_info->delete_unused_bgs_mutex);
>> >> > +                               ret = PTR_ERR(trans);
>> >> > +                               goto error;
>> >> > +                       }
>> >> > +
>> >> > +                       ret = btrfs_force_chunk_alloc(trans,
>> >> > + chunk_root, 1);
>> >>
>> >> Can we please use the symbol BTRFS_BLOCK_GROUP_DATA instead of 1?
>> >>
>> > Thanks, will change in v2.
>> >
>> >
>> >> > +                       if (ret < 0) {
>> >> > +
>> >> mutex_unlock(&fs_info->delete_unused_bgs_mutex);
>> >> > +                               goto error;
>> >> > +                       }
>> >> > +
>> >> > +                       btrfs_end_transaction(trans, chunk_root);
>> >> > +                       chunk_reserved = 1;
>> >> > +               }
>> >>
>> >> Can we do this logic only if the block group is a data one? I.e. no
>> >> point allocating a data block group if our balance only touches
>> >> metadata ones (due to some filter for e.g.).
>> >>
>> > Thanks for point out it, will change in v2.
>>
>> I find it somewhat awkward that we always allocate a new data block group no
>> matter what. Some balance operations that used to succeed in the past may
>> now fail with -ENOSPC for example...
>>
>> How about making this simpler and not so special for data block groups, like the
>> following (compile tested only):
>>
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 644e070..067b1eb
>> 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -2774,6 +2774,8 @@ static int btrfs_relocate_chunk(struct btrfs_root
>> *root, u64 chunk_offset)
>>         struct btrfs_root *extent_root;
>>         struct btrfs_trans_handle *trans;
>>         int ret;
>> +       struct btrfs_block_group_cache *bg;
>> +       bool remove = true;
>>
>>         root = root->fs_info->chunk_root;
>>         extent_root = root->fs_info->extent_root; @@ -2803,6 +2805,23
>> @@ static int btrfs_relocate_chunk(struct btrfs_root *root, u64 chunk_offset)
>>         if (ret)
>>                 return ret;
>>
>> +       bg = btrfs_lookup_block_group(root->fs_info, chunk_offset);
>> +       ASSERT(bg);
>> +       down_read(&bg->space_info->groups_sem);
>> +       /*
>> +        * Do not remove the last block group of a kind to prevent losing
>> +        * raid profile information for future chunk allocations.
>> +        */
>> +       if (bg->list.next == bg->list.prev)
>> +               remove = false;
>> +       up_read(&bg->space_info->groups_sem);
>> +       if (!remove)
>> +               btrfs_dec_block_group_ro(extent_root, bg);
>> +       btrfs_put_block_group(bg);
>> +
>> +       if (!remove)
>> +               return 0;
>> +
>>         trans = btrfs_start_transaction(root, 0);
>>         if (IS_ERR(trans)) {
>>                 ret = PTR_ERR(trans);
>>
>
> Thanks for your detailed review!
>
> Reason of creating new bg is:
> Balance operation may be used to change raid-profile of the filesystem.
> If we want to change filesystem form raid1 to raid5, we need:
> 1: delete all raid1 bgs
> 2: move all data to raid5 bg if data exist in filesystem
> 3: reserve only one blank raid5 bg if no data in filesystem

I see. Thanks.

>
> If we use similar operation as patch 1/2(not delete lattest blockgroup),
> we'll have following problem:
> 1: the old raid1 blockgroups are not all-deleted
> 2: if no data in filesystem, the profile will not changed from raid1 to raid5.
>
> I understand your worry of "NO_SPACE" when create additional bg,
> and I also considered it in making patch, but I choose to use this way because:
> 1: balance operation had check free space before operation
>   (In front of __btrfs_balance)
> 2: for filesystem with data, we have to create target-chunk in balance operation,
>   this patch only make "creating-chunk" earlier, and the created chunk will be used
>   to save data in balance operation, and reduce one chunk-allocate in balance operation.
> 3: for a blank filesystem, it is necessary to create a blank chunk with of target raid profile.
>   the old code hadn't create it, and this patch created. It is right operation even if
>   cause no-space. Actually, create a chunk in empty filesystem rarely cause no-space,
>   plus we have free-space check in 1.
> 4: 1~3 ensure this patch rarely cause additional no-space problem in logic.
>   And if it really caused additional no-space(if out of my consideration),
>   We can change code of 1 to avoid it.
>
> Thanks
> Zhaolei
>
>> (also at https://friendpaste.com/5IeAIIzBv3oKhureKfvjwm)
>>
>> thanks
>>
>>
>> >
>> >> Also, can't this be ineffective when the data block group we allocate
>> >> ends up with a key  in the chunk_root that is lower than the key we
>> >> found in the current iteration? I.e., key found in current iteration
>> >> has object id B, we allocate a new block group which gets a  key with
>> >> object id A, where A < B and the next iteration of our loop sees key
>> >> A, deletes the respective block group A if it's empty. In the end we
>> >> have no data block groups, assuming that before A there are no other
>> non-empty data block groups.
>> >> Your example works because there's no free space before the offset
>> >> where the chunk starts in the device.
>> >>
>> > New chunk will always use increased logic address, even if there are
>> > "hole" before, so A's logic address will always >B.
>> > And current code of balance also use this feature to avoid balance
>> > new-created chunks(which was created by balance operation itself).
>> >
>> > Thanks
>> > Zhaolei
>> >
>> >> thanks
>> >>
>> >> > +
>> >> >                 ret = btrfs_relocate_chunk(chunk_root,
>> >> >                                            found_key.offset);
>> >> >                 mutex_unlock(&fs_info->delete_unused_bgs_mutex);
>> >> > --
>> >> > 1.8.5.1
>> >> >
>> >> > --
>> >> > To unsubscribe from this list: send the line "unsubscribe linux-btrfs"
>> >> > in the body of a message to majordomo@vger.kernel.org More
>> >> > majordomo info at  http://vger.kernel.org/majordomo-info.html
>> >>
>> >>
>> >>
>> >> --
>> >> Filipe David Manana,
>> >>
>> >> "Reasonable men adapt themselves to the world.
>> >>  Unreasonable men adapt the world to themselves.
>> >>  That's why all progress depends on unreasonable men."
>> >
>>
>>
>>
>> --
>> Filipe David Manana,
>>
>> "Reasonable men adapt themselves to the world.
>>  Unreasonable men adapt the world to themselves.
>>  That's why all progress depends on unreasonable men."
>



-- 
Filipe David Manana,

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."

Re: [PATCH 1/2] btrfs: Fix lost-data-profile caused by auto removing bg

[Filipe Manana]

On Tue, Sep 29, 2015 at 2:51 PM, Zhao Lei <zhaolei@cn.fujitsu.com> wrote:
> Reproduce:
>  (In integration-4.3 branch)
>
>  TEST_DEV=(/dev/vdg /dev/vdh)
>  TEST_DIR=/mnt/tmp
>
>  umount "$TEST_DEV" >/dev/null
>  mkfs.btrfs -f -d raid1 "${TEST_DEV[@]}"
>
>  mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
>  umount "$TEST_DEV"
>
>  mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
>  btrfs filesystem usage $TEST_DIR
>
> We can see the data chunk changed from raid1 to single:
>  # btrfs filesystem usage $TEST_DIR
>  Data,single: Size:8.00MiB, Used:0.00B
>     /dev/vdg        8.00MiB
>  #
>
> Reason:
>  When a empty filesystem mount with -o nospace_cache, the last
>  data blockgroup will be auto-removed in umount.
>
>  Then if we mount it again, there is no data chunk in the
>  filesystem, so the only available data profile is 0x0, result
>  is all new chunks are created as single type.
>
> Fix:
>  Don't auto-delete last blockgroup for a raid type.
>
> Test:
>  Test by above script, and confirmed the logic by debug output.
>
> Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
> ---
>  fs/btrfs/extent-tree.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 79a5bd9..3505649 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -10012,7 +10012,8 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
>                                                bg_list);
>                 space_info = block_group->space_info;
>                 list_del_init(&block_group->bg_list);
> -               if (ret || btrfs_mixed_space_info(space_info)) {
> +               if (ret || btrfs_mixed_space_info(space_info) ||
> +                   block_group->list.next == block_group->list.prev) {

This isn't race free. The list block_group->list is protected by the
groups_sem semaphore. Need to take before doing this check.
You can do that in the "if" statement below this one, where we're
holding &space_info->groups_sem [1]

thanks

[1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/btrfs/extent-tree.c?id=refs/tags/v4.3-rc3#n10021

>                         btrfs_put_block_group(block_group);
>                         continue;
>                 }
> --
> 1.8.5.1
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html



-- 
Filipe David Manana,

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."

RE: [PATCH 1/2] btrfs: Fix lost-data-profile caused by auto removing bg

[Zhao Lei]

Hi, Filipe Manana

> -----Original Message-----
> From: linux-btrfs-owner@vger.kernel.org
> [mailto:linux-btrfs-owner@vger.kernel.org] On Behalf Of Filipe Manana
> Sent: Wednesday, September 30, 2015 3:43 PM
> To: Zhao Lei <zhaolei@cn.fujitsu.com>
> Cc: linux-btrfs@vger.kernel.org
> Subject: Re: [PATCH 1/2] btrfs: Fix lost-data-profile caused by auto removing bg
> 
> On Tue, Sep 29, 2015 at 2:51 PM, Zhao Lei <zhaolei@cn.fujitsu.com> wrote:
> > Reproduce:
> >  (In integration-4.3 branch)
> >
> >  TEST_DEV=(/dev/vdg /dev/vdh)
> >  TEST_DIR=/mnt/tmp
> >
> >  umount "$TEST_DEV" >/dev/null
> >  mkfs.btrfs -f -d raid1 "${TEST_DEV[@]}"
> >
> >  mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
> >  umount "$TEST_DEV"
> >
> >  mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
> >  btrfs filesystem usage $TEST_DIR
> >
> > We can see the data chunk changed from raid1 to single:
> >  # btrfs filesystem usage $TEST_DIR
> >  Data,single: Size:8.00MiB, Used:0.00B
> >     /dev/vdg        8.00MiB
> >  #
> >
> > Reason:
> >  When a empty filesystem mount with -o nospace_cache, the last  data
> > blockgroup will be auto-removed in umount.
> >
> >  Then if we mount it again, there is no data chunk in the  filesystem,
> > so the only available data profile is 0x0, result  is all new chunks
> > are created as single type.
> >
> > Fix:
> >  Don't auto-delete last blockgroup for a raid type.
> >
> > Test:
> >  Test by above script, and confirmed the logic by debug output.
> >
> > Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
> > ---
> >  fs/btrfs/extent-tree.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index
> > 79a5bd9..3505649 100644
> > --- a/fs/btrfs/extent-tree.c
> > +++ b/fs/btrfs/extent-tree.c
> > @@ -10012,7 +10012,8 @@ void btrfs_delete_unused_bgs(struct
> btrfs_fs_info *fs_info)
> >                                                bg_list);
> >                 space_info = block_group->space_info;
> >                 list_del_init(&block_group->bg_list);
> > -               if (ret || btrfs_mixed_space_info(space_info)) {
> > +               if (ret || btrfs_mixed_space_info(space_info) ||
> > +                   block_group->list.next == block_group->list.prev)
> > + {
> 
> This isn't race free. The list block_group->list is protected by the groups_sem
> semaphore. Need to take before doing this check.

Thanks for pointing out this.

> You can do that in the "if" statement below this one, where we're holding
> &space_info->groups_sem [1]
> 
It is hard to do check in btrfs_remove_block_group(), because it is common
function used by both balance and auto-remove bg.

For balance operation, we can remove lattest bg in some case, or we need
add additional argument to separate these two operation(complex).

So I decided to take groups_sem semaphore in place of checking.
Thanks for notice this lock problem.

btw, could I add your signed-off-by or reviewed-by in patch 2/2?

Thanks
Zhaolei

> thanks
> 
> [1]
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/btrfs/exte
> nt-tree.c?id=refs/tags/v4.3-rc3#n10021
> 
> >                         btrfs_put_block_group(block_group);
> >                         continue;
> >                 }
> > --
> > 1.8.5.1
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-btrfs"
> > in the body of a message to majordomo@vger.kernel.org More majordomo
> > info at  http://vger.kernel.org/majordomo-info.html
> 
> 
> 
> --
> Filipe David Manana,
> 
> "Reasonable men adapt themselves to the world.
>  Unreasonable men adapt the world to themselves.
>  That's why all progress depends on unreasonable men."
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body
> of a message to majordomo@vger.kernel.org More majordomo info at
> http://vger.kernel.org/majordomo-info.html

Re: [PATCH 1/2] btrfs: Fix lost-data-profile caused by auto removing bg

[Filipe Manana]

On Wed, Sep 30, 2015 at 11:06 AM, Zhao Lei <zhaolei@cn.fujitsu.com> wrote:
> Hi, Filipe Manana
>
>> -----Original Message-----
>> From: linux-btrfs-owner@vger.kernel.org
>> [mailto:linux-btrfs-owner@vger.kernel.org] On Behalf Of Filipe Manana
>> Sent: Wednesday, September 30, 2015 3:43 PM
>> To: Zhao Lei <zhaolei@cn.fujitsu.com>
>> Cc: linux-btrfs@vger.kernel.org
>> Subject: Re: [PATCH 1/2] btrfs: Fix lost-data-profile caused by auto removing bg
>>
>> On Tue, Sep 29, 2015 at 2:51 PM, Zhao Lei <zhaolei@cn.fujitsu.com> wrote:
>> > Reproduce:
>> >  (In integration-4.3 branch)
>> >
>> >  TEST_DEV=(/dev/vdg /dev/vdh)
>> >  TEST_DIR=/mnt/tmp
>> >
>> >  umount "$TEST_DEV" >/dev/null
>> >  mkfs.btrfs -f -d raid1 "${TEST_DEV[@]}"
>> >
>> >  mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
>> >  umount "$TEST_DEV"
>> >
>> >  mount -o nospace_cache "$TEST_DEV" "$TEST_DIR"
>> >  btrfs filesystem usage $TEST_DIR
>> >
>> > We can see the data chunk changed from raid1 to single:
>> >  # btrfs filesystem usage $TEST_DIR
>> >  Data,single: Size:8.00MiB, Used:0.00B
>> >     /dev/vdg        8.00MiB
>> >  #
>> >
>> > Reason:
>> >  When a empty filesystem mount with -o nospace_cache, the last  data
>> > blockgroup will be auto-removed in umount.
>> >
>> >  Then if we mount it again, there is no data chunk in the  filesystem,
>> > so the only available data profile is 0x0, result  is all new chunks
>> > are created as single type.
>> >
>> > Fix:
>> >  Don't auto-delete last blockgroup for a raid type.
>> >
>> > Test:
>> >  Test by above script, and confirmed the logic by debug output.
>> >
>> > Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
>> > ---
>> >  fs/btrfs/extent-tree.c | 3 ++-
>> >  1 file changed, 2 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index
>> > 79a5bd9..3505649 100644
>> > --- a/fs/btrfs/extent-tree.c
>> > +++ b/fs/btrfs/extent-tree.c
>> > @@ -10012,7 +10012,8 @@ void btrfs_delete_unused_bgs(struct
>> btrfs_fs_info *fs_info)
>> >                                                bg_list);
>> >                 space_info = block_group->space_info;
>> >                 list_del_init(&block_group->bg_list);
>> > -               if (ret || btrfs_mixed_space_info(space_info)) {
>> > +               if (ret || btrfs_mixed_space_info(space_info) ||
>> > +                   block_group->list.next == block_group->list.prev)
>> > + {
>>
>> This isn't race free. The list block_group->list is protected by the groups_sem
>> semaphore. Need to take before doing this check.
>
> Thanks for pointing out this.
>
>> You can do that in the "if" statement below this one, where we're holding
>> &space_info->groups_sem [1]
>>
> It is hard to do check in btrfs_remove_block_group(), because it is common
> function used by both balance and auto-remove bg.

I didn't say to move it to or touch btrfs_remove_block_group() at all.
What I meant is to do check still inside btrfs_delete_unused_bgs but
in the other "if" statement that is done while holding the groups
semaphore, i.e.:

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 9f96042..627ac3b 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -10022,7 +10022,8 @@ void btrfs_delete_unused_bgs(struct
btrfs_fs_info *fs_info)
                spin_lock(&block_group->lock);
                if (block_group->reserved ||
                    btrfs_block_group_used(&block_group->item) ||
-                   block_group->ro) {
+                   block_group->ro ||
+                   lock_group->list.next == block_group->list.prev) {
                        /*
                         * We want to bail if we made new allocations or have
                         * outstanding allocations in this block group.  We do


>
> For balance operation, we can remove lattest bg in some case, or we need
> add additional argument to separate these two operation(complex).
>
> So I decided to take groups_sem semaphore in place of checking.

Not sure I follow. The problem I was pointing is doing the check
without holding the groups semaphore.

> Thanks for notice this lock problem.
>
> btw, could I add your signed-off-by or reviewed-by in patch 2/2?

Yeah, once I see the updated version I can add a reviewed-by tag.

thanks

>
> Thanks
> Zhaolei
>
>> thanks
>>
>> [1]
>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/btrfs/exte
>> nt-tree.c?id=refs/tags/v4.3-rc3#n10021
>>
>> >                         btrfs_put_block_group(block_group);
>> >                         continue;
>> >                 }
>> > --
>> > 1.8.5.1
>> >
>> > --
>> > To unsubscribe from this list: send the line "unsubscribe linux-btrfs"
>> > in the body of a message to majordomo@vger.kernel.org More majordomo
>> > info at  http://vger.kernel.org/majordomo-info.html
>>
>>
>>
>> --
>> Filipe David Manana,
>>
>> "Reasonable men adapt themselves to the world.
>>  Unreasonable men adapt the world to themselves.
>>  That's why all progress depends on unreasonable men."
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body
>> of a message to majordomo@vger.kernel.org More majordomo info at
>> http://vger.kernel.org/majordomo-info.html
>



-- 
Filipe David Manana,

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."