Re: [PATCH] btrfs/179: optimize remove file selection

[Josef Bacik <josef@toxicpanda.com>]

On Thu, Aug 17, 2023 at 02:13:17PM +0900, Naohiro Aota wrote:
> Currently, we use "ls ... | sort -R | head -n1" to choose a removing
> victim. It sorts the files with "ls", sort it randomly and pick the first
> line, which wastes the "ls" sort.
> 
> Also, using "sort -R | head -n1" is inefficient. For example, in a
> directory with 1000000 files, it takes more than 15 seconds to pick a file.
> 
>   $ time bash -c "ls -U | sort -R | head -n 1 >/dev/null"
>   bash -c "ls -U | sort -R | head -n 1 >/dev/null"  15.38s user 0.14s system 99% cpu 15.536 total
> 
>   $ time bash -c "ls -U | shuf -n 1 >/dev/null"
>   bash -c "ls -U | shuf -n 1 >/dev/null"  0.30s user 0.12s system 138% cpu 0.306 total
> 
> So, just use "ls -U" and "shuf -n 1" to choose a victim.
> 
> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef