Re: [PATCH 0/7] btrfs: per-fs compression workspace manager

[David Sterba <dsterba@suse.cz>]

On Thu, Aug 14, 2025 at 03:03:19PM +0930, Qu Wenruo wrote:
> Currently btrfs utilizes the following components at a per-module basis:
> 
> - Folios pool
>   A per-module pool for compressed data.
>   All folios in the pool are page sized.
> 
> - Workspace
>   A workspace is a compression algorithm specific structure, providing
>   things like extra memory buffer and compression level handling.
> 
> - Workspace manager
>   The workspace manager is managing the above workspaces for each
>   algorithm.
> 
> All the folio pool/workspaces are using the fixed PAGE_SIZE buffer size,
> this is fine for now as even for block size (bs) < page size (ps) cases,
> a larger buffer size won't cause huge problems except wasting memories.
> 
> However if we're going to support bs > ps, this fixed PAGE_SIZE buffer
> and per-module shared folios pool/workspaces will not work at all.
> 
> To address this problem, this series will move the workspace and
> workspace manager into a per-fs basis, so that different fses (with
> different block size) can have their own workspaces.
> 
> This brings a small memory usage reduce for bs < ps cases.
> Now zlib/lzo/zstd will only allocate buffer using block size.
> 
> This is especially useful for lzo compression algorithm, as lzo is an
> one-short compression algorithm, it doesn't support multi-shot (aka,
> swapping input/output buffer halfway) compress/decompress.
> 
> Thus btrfs goes per-block compression for LZO, and compressed result
> will never go larger than a block (or btrfs will just give up).
> In that case, a 64K page sized buffer will waste 7/8th of the buffer.
> 
> This is part 1 of the preparation for btrfs bs > ps support.
> 
> Qu Wenruo (7):
>   btrfs: add an fs_info parameter for compression workspace manager
>   btrfs: add workspace manager initialization for zstd
>   btrfs: add generic workspace manager initialization
>   btrfs: migrate to use per-fs workspace manager
>   btrfs: cleanup the per-module workspace managers
>   btrfs: rename btrfs_compress_op to btrfs_compress_levels
>   btrfs: reduce workspace buffer space to block size

Reviewed-by: David Sterba <dsterba@suse.com>