From 0a6dcd42353b96ab4a74796aed1541591de5890c Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Mon, 11 Aug 2025 09:43:42 +0930 Subject: [PATCH] btrfs: use blocksize to check if compression is making things larger [BEHAVIOR DIFFERENCE BETWEEN COMPRESSION ALGOS] Currently LZO compression algorithm will check if we're making the compressed data larger after compressing more than 2 blocks. But zlib and zstd do the same checks after compressing more than 8192 bytes. This is not a big deal, but since we're already supporting larger block size (e.g. 64K block size if page size is also 64K), this check is not suitable for all block sizes. For example, if our page and block size are both 16KiB, and after the first block compressed using zlib, the resulted compressed data is slightly larger than 16KiB, we will immediately abort the compression. This makes zstd and zlib compression algorithms to behave slightly different from LZO, which only aborts after compressing two blocks. [ENHANCEMENT] To unify the behavior, only abort the compression after compressing at least two blocks. Reviewed-by: Anand Jain Signed-off-by: Qu Wenruo Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/zlib.c | 3 ++- fs/btrfs/zstd.c | 3 ++- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/zlib.c b/fs/btrfs/zlib.c index 21af68f93a2d1..33dc7e7b5c364 100644 --- a/fs/btrfs/zlib.c +++ b/fs/btrfs/zlib.c @@ -148,6 +148,7 @@ int zlib_compress_folios(struct list_head *ws, struct btrfs_inode *inode, unsigned long len = *total_out; unsigned long nr_dest_folios = *out_folios; const unsigned long max_out = nr_dest_folios * PAGE_SIZE; + const u32 blocksize = inode->root->fs_info->sectorsize; const u64 orig_end = start + len; *out_folios = 0; @@ -234,7 +235,7 @@ int zlib_compress_folios(struct list_head *ws, struct btrfs_inode *inode, } /* we're making it bigger, give up */ - if (workspace->strm.total_in > 8192 && + if (workspace->strm.total_in > blocksize * 2 && workspace->strm.total_in < workspace->strm.total_out) { ret = -E2BIG; diff --git a/fs/btrfs/zstd.c b/fs/btrfs/zstd.c index 00159e0e921ea..d521187336a59 100644 --- a/fs/btrfs/zstd.c +++ b/fs/btrfs/zstd.c @@ -400,6 +400,7 @@ int zstd_compress_folios(struct list_head *ws, struct btrfs_inode *inode, unsigned long len = *total_out; const unsigned long nr_dest_folios = *out_folios; const u64 orig_end = start + len; + const u32 blocksize = inode->root->fs_info->sectorsize; unsigned long max_out = nr_dest_folios * PAGE_SIZE; unsigned int cur_len; @@ -456,7 +457,7 @@ int zstd_compress_folios(struct list_head *ws, struct btrfs_inode *inode, } /* Check to see if we are making it bigger */ - if (tot_in + workspace->in_buf.pos > 8192 && + if (tot_in + workspace->in_buf.pos > blocksize * 2 && tot_in + workspace->in_buf.pos < tot_out + workspace->out_buf.pos) { ret = -E2BIG; -- 2.47.3