Re: Regression in v5.14-rc1: f2165627319f btrfs: compression: don't try to compress if we don't have enough pages

Zygo Blaxell
2021-08-22T06:02:29Z

On Sun, Aug 22, 2021 at 01:51:15AM -0400, Zygo Blaxell wrote:

I trimmed my cut+paste too eagerly...

> Before this commit:
>
> # head /dev/zero -c 4095 > inline
> # compsize inline
Processed 1 file, 0 regular extents (0 refs), 1 inline.
> Type Perc Disk Usage Uncompressed Referenced
> TOTAL 0% 18B 3.9K 3.9K
> zstd 0% 18B 3.9K 3.9K
>
> After this commit:
>
> # head /dev/zero -c 4095 > inline
> # compsize inline
> Processed 1 file, 1 regular extents (1 refs), 0 inline.
> Type Perc Disk Usage Uncompressed Referenced
> TOTAL 100% 4.0K 4.0K 4.0K
> none 100% 4.0K 4.0K 4.0K
>
> This change makes the metadata sizes of trees of small files (e.g. source
> checkouts) blow up.
>
> It looks like we need to look at the offset of the extent, as well as
> its length.