Re: [PATCH 3/3] btrfs: use u8 type for btrfs_block_rsv::type

[David Sterba <dsterba@suse.cz>]

On Tue, Jun 28, 2022 at 07:15:14AM +0000, Johannes Thumshirn wrote:
> On 27.06.22 18:45, David Sterba wrote:
> > On Mon, Jun 27, 2022 at 06:51:30AM +0000, Johannes Thumshirn wrote:
> >> On 24.06.22 16:15, David Sterba wrote:
> >>> diff --git a/fs/btrfs/block-rsv.h b/fs/btrfs/block-rsv.h
> >>> index 0702d4087ff6..bb449c75ee4c 100644
> >>> --- a/fs/btrfs/block-rsv.h
> >>> +++ b/fs/btrfs/block-rsv.h
> >>> @@ -27,7 +27,8 @@ struct btrfs_block_rsv {
> >>>  	spinlock_t lock;
> >>>  	bool full;
> >>>  	bool failfast;
> >>> -	unsigned short type;
> >>> +	/* Block reserve type, one of BTRFS_BLOCK_RSV_* */
> >>> +	u8 type;
> >>>  
> >>
> >> Is there any reason to not use the enum?
> > 
> > Enum would be 'int', 4 bytes to the space optimization would be
> > lost. Enum types can be shortened as
> > 
> > 	enum btrfs_reserve type:8
> > 
> > but I'm not sure it's an improvement.
> > 
> 
> Using an enum would give some type safety (I think -Wenum-compare is 
> on by default in the kernel). Packing that enum would give us the 1 byte
> size you're looking for.

Yeah I'll go with the named enum and :8 in the structure.