Reviewed-by: Goldwyn Rodrigues
On 10/17/2016 08:31 PM, Qu Wenruo wrote:
> Add explain how btrfs qgroup works.
>
> Qgroup is split into 3 main phrases:
> 1) Reserve
>To ensure qgroup doesn't exceed its limit
>
> 2) Trace
>To info qgroup to trace which extent
>
> 3) Account
>Calculate qgroup number change for each traced extent.
>
> This should save quite some time for new developers.
>
> Signed-off-by: Qu Wenruo
> ---
> fs/btrfs/qgroup.h | 28
> 1 file changed, 28 insertions(+)
>
> diff --git a/fs/btrfs/qgroup.h b/fs/btrfs/qgroup.h
> index 1bc64c8..a72bf21 100644
> --- a/fs/btrfs/qgroup.h
> +++ b/fs/btrfs/qgroup.h
> @@ -23,6 +23,34 @@
> #include "delayed-ref.h"
>
> /*
> + * Btrfs qgroup overview
> + *
> + * Btrfs qgroup splits into 3 main part:
> + * 1) Reserve
> + *Reserve metadata/data space for incoming operations
> + *Affect how qgroup limit works
> + *
> + * 2) Trace
> + *Tell btrfs qgroup to trace dirty extents.
> + *
> + *Dirty extents including:
> + *- Newly allocated extents
> + *- Extents going to be deleted (in this trans)
> + *- Extents whose owner is going to be modified
> + *
> + *This is the main part affects whether qgroup numbers will stay
> + *consistent.
> + *Btrfs qgroup can trace clean extents and won't cause any problem,
> + *but it will consume extra CPU time, it should be avoided if possible.
> + *
> + * 3) Account
> + *Btrfs qgroup will updates its numbers, based on dirty extents traced
> + *in previous step.
> + *
> + *Normally at qgroup rescan and transaction commit time.
> + */
> +
> +/*
> * Record a dirty extent, and info qgroup to update quota on it
> * TODO: Use kmem cache to alloc it.
> */
>
--
Goldwyn
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