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List:       linux-btrfs
Subject:    Re: space_cache=v1 and v2 at the time time?
From:       Hans van Kranenburg <hans () knorrie ! org>
Date:       2020-05-28 21:04:07
Message-ID: c33f3305-a265-d2a4-75e3-9bdd850604f8 () knorrie ! org
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Hi,

On 5/27/20 4:12 AM, Chris Murphy wrote:
> What are the implications of not clearing v1 before enabling v2?
> 
> From btrfs insp dump-t, I still see the v1 bitmaps present:
> 
> root tree
> leaf 6468501504 items 42 free space 9246 generation 22 owner ROOT_TREE
> leaf 6468501504 flags 0x1(WRITTEN) backref revision 1
> ...
>     item 30 key (FREE_SPACE UNTYPED 22020096) itemoff 11145 itemsize 41
>         location key (256 INODE_ITEM 0)
>         cache generation 17 entries 0 bitmaps 0
>     item 31 key (FREE_SPACE UNTYPED 1095761920) itemoff 11104 itemsize 41
>         location key (257 INODE_ITEM 0)
>         cache generation 17 entries 0 bitmaps 0
> ...
> 
> 
> And later the free space tree:
> 
> free space tree key (FREE_SPACE_TREE ROOT_ITEM 0)
> leaf 6471073792 items 39 free space 15196 generation 22 owner FREE_SPACE_TREE
> leaf 6471073792 flags 0x1(WRITTEN) backref revision 1
> fs uuid 3c464210-08c7-4cf0-b175-e4b781ebea19
> chunk uuid f1d18732-7c3d-401c-8637-e7d4d9c7a0b8
>     item 0 key (1048576 FREE_SPACE_INFO 4194304) itemoff 16275 itemsize 8
>         free space info extent count 2 flags 0
>     item 1 key (1048576 FREE_SPACE_EXTENT 16384) itemoff 16275 itemsize 0
>         free space extent
>     item 2 key (1081344 FREE_SPACE_EXTENT 4161536) itemoff 16275 itemsize 0
>         free space extent
> ...
> 
> I was surprised there's no warning when I use space_cache=v2 without
> first clearing v1.

It's just sitting there, occupying some space, doing nothing.

Hans
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