Re: [PATCH v2 14/14] f2fs: make compressed files compatible with large folio

[Chao Yu]

On 9/15/26 12:25, Nanzhe Zhao wrote:
> The compression flag is the hint indicates that the inode can be
> compressed, when the inode is using large folio, we expected it keeps
> using the large folio read/write paths and its data stays uncompressed
> on disk until the inode is evicted and re-read
> 
> Let f2fs_write_begin() skip the compression overwrite preparation for
> such inodes and remove the compressed-file gate in
> f2fs_read_data_large_folio() so the data is simply read/written as
> regular blocks.
> 
> For the same reason, reject F2FS_IOC_COMPRESS_FILE with -EOPNOTSUPP
> once the inode mapping is switched to large folios.
> 
> Signed-off-by: Nanzhe Zhao <zhaonanzhe@xxxxxxxxxx>
> ---
>  Documentation/filesystems/f2fs.rst | 10 ++++++++++
>  fs/f2fs/compress.c                 |  2 ++
>  fs/f2fs/data.c                     |  9 ++-------
>  fs/f2fs/file.c                     |  7 +++++++
>  4 files changed, 21 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
> index 771216f45207..b4f436ffd9ac 100644
> --- a/Documentation/filesystems/f2fs.rst
> +++ b/Documentation/filesystems/f2fs.rst
> @@ -941,6 +941,16 @@ Compression implementation
>    reserved via ioctl(F2FS_IOC_RESERVE_COMPRESS_BLOCKS) or the file size is
>    truncated to zero.
>  
> +- Compression and large folios are not effective at the same time on a file:
> +  a compressed inode does not use large folios, while an inode which is
> +  using large folios keeps its data uncompressed on disk.  If the compression
> +  flag is set on an inode that is already using large folios, the flag works
> +  as a hint until the inode is evicted: the inode keeps using the large folio
> +  read/write paths, f2fs_write_begin() skips the compression overwrite
> +  preparation, and ioctl(F2FS_IOC_COMPRESS_FILE) fails with -EOPNOTSUPP.
> +  Once the inode is evicted and read back, it uses order-0 folios again and
> +  compression is applied as usual.
> +
>  Compress metadata layout::
>  
>  				[Dnode Structure]
> diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
> index b130e43b4566..fa0f8449a12c 100644
> --- a/fs/f2fs/compress.c
> +++ b/fs/f2fs/compress.c
> @@ -78,6 +78,8 @@ bool f2fs_is_compressed_page(struct folio *folio)
>  		return false;
>  	if (folio_test_f2fs_nonpointer(folio))
>  		return false;
> +	if (f2fs_folio_has_ffs(folio))
> +		return false;
>  
>  	f2fs_bug_on(F2FS_F_SB(folio),
>  		*((u32 *)folio->private) != F2FS_COMPRESSED_PAGE_MAGIC);
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index c9dba8d0ad3d..f5421334ecf3 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -2941,12 +2941,6 @@ static int f2fs_read_data_large_folio(struct inode *inode,
>  	int ret = 0;
>  	bool folio_in_bio = false;
>  
> -	if (f2fs_compressed_file(inode)) {
> -		if (folio)
> -			folio_unlock(folio);
> -		return -EOPNOTSUPP;
> -	}
> -
>  	map.m_seg_type = NO_CHECK_TYPE;
>  
>  	if (rac)
> @@ -4828,7 +4822,8 @@ static int f2fs_write_begin(const struct kiocb *iocb,
>  	}
>  
>  #ifdef CONFIG_F2FS_FS_COMPRESSION
> -	if (f2fs_compressed_file(inode)) {
> +	if (f2fs_compressed_file(inode) &&
> +	    !mapping_large_folio_support(inode->i_mapping)) {
>  		int ret;
>  		struct page *page;
>  
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index db71cadefabd..c5cb0b0384b6 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -5002,6 +5002,13 @@ static int f2fs_ioc_compress_file(struct file *filp)
>  	if (!(filp->f_mode & FMODE_WRITE))
>  		return -EBADF;
>  
> +	/*
> +	 * The mapping is already using large folios, where the data is kept
> +	 * uncompressed, so refuse to start compressing the file.
> +	 */
> +	if (mapping_large_folio_support(inode->i_mapping))

It needs to print log here to give notice.

e.g "not support if large folio bit is set, drop inode cache to unset the flag and retry" ?

Thanks,

> +		return -EOPNOTSUPP;
> +
>  	f2fs_balance_fs(sbi, true);
>  
>  	ret = mnt_want_write_file(filp);