Re: [PATCH v4] btrfs: zstd: enable negative compression levels mount option

[David Sterba]

On Thu, Jan 30, 2025 at 06:58:19PM +0100, Daniel Vacek wrote:
> This patch allows using the fast modes (negative compression levels) of zstd
> as a mount option.
> 
> As per the results, the compression ratio is lower:
> 
> for level in {-15..-1} 1 2 3; \
> do printf "level %3d\n" $level; \
>   mount -o compress=zstd:$level /dev/sdb /mnt/test/; \
>   grep sdb /proc/mounts; \
>   cp -r /usr/bin       /mnt/test/; sync; compsize /mnt/test/bin; \
>   cp -r /usr/share/doc /mnt/test/; sync; compsize /mnt/test/doc; \
>   cp    enwik9         /mnt/test/; sync; compsize /mnt/test/enwik9; \
>   cp    linux-6.13.tar /mnt/test/; sync; compsize /mnt/test/linux-6.13.tar; \
>   rm -r /mnt/test/{bin,doc,enwik9,linux-6.13.tar}; \
>   umount /mnt/test/; \
> done |& tee results | \
> awk '/^level/{print}/^TOTAL/{print$3"\t"$2"  |"}' | paste - - - - -
> 
> 		266M	bin  |	45M	doc  |	953M	wiki |	1.4G	source
> =============================+===============+===============+===============+
> level -15	180M	67%  |	30M	68%  |	694M	72%  |	598M	40%  |
> level -14	180M	67%  |	30M	67%  |	683M	71%  |	581M	39%  |
> level -13	177M	66%  |	29M	66%  |	671M	70%  |	566M	38%  |
> level -12	174M	65%  |	29M	65%  |	658M	69%  |	548M	37%  |
> level -11	174M	65%  |	28M	64%  |	645M	67%  |	530M	35%  |
> level -10	171M	64%  |	28M	62%  |	631M	66%  |	512M	34%  |
> level  -9	165M	62%  |	27M	61%  |	615M	64%  |	493M	33%  |
> level  -8	161M	60%  |	27M	59%  |	598M	62%  |	475M	32%  |
> level  -7	155M	58%  |	26M	58%  |	582M	61%  |	457M	30%  |
> level  -6	151M	56%  |	25M	56%  |	565M	59%  |	437M	29%  |
> level  -5	145M	54%  |	24M	55%  |	545M	57%  |	417M	28%  |
> level  -4	139M	52%  |	23M	52%  |	520M	54%  |	391M	26%  |
> level  -3	135M	50%  |	22M	50%  |	495M	51%  |	369M	24%  |
> level  -2	127M	47%  |	22M	48%  |	470M	49%  |	349M	23%  |
> level  -1	120M	45%  |	21M	47%  |	452M	47%  |	332M	22%  |
> level   1	110M	41%  |	17M	39%  |	362M	38%  |	290M	19%  |
> level   2	106M	40%  |	17M	38%  |	349M	36%  |	288M	19%  |
> level   3	104M	39%  |	16M	37%  |	340M	35%  |	276M	18%  |
> 
> Signed-off-by: Daniel Vacek <neelx@xxxxxxxx>
> ---
> Changes in v4:
>  * Fix a bug with workspace lru_list.
>  * Keep the levels down to -15 as agreed.

Thanks, I'll add the patch to for-next soon. The information about times
is only a changelog update so this can be done later once we have it.