Re: [f2fs-dev] [PATCH] f2fs: avoid unused block when dio write in LFS mode

[Chao Yu <chao@kernel.org>]

On 2024/8/1 15:47, Daejun Park wrote:
> This patch addresses the problem that when using LFS mode, unused blocks
> may occur in f2fs_map_blocks() during block allocation for dio writes.
> 
> If a new section is allocated during block allocation, it will not be
> included in the map struct by map_is_mergeable() if the LBA of the

I didn't get it, why below condition in map_is_mergeable() can not catch this
case? Can you please explain more?

	if (map->m_pblk != NEW_ADDR && blkaddr == (map->m_pblk + ofs))
		return true;

Thanks,

> allocated block is not contiguous. However, the block already allocated
> in this process will remain unused due to the LFS mode.
> 
> This patch avoids the possibility of unused blocks by escaping
> f2fs_map_blocks() when allocating the last block in a section.
> 
> Signed-off-by: Daejun Park <daejun7.park@samsung.com>
> ---
>   fs/f2fs/data.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index b6dcb3bcaef7..b27a3f448f32 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1711,6 +1711,19 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
>   		dn.ofs_in_node = end_offset;
>   	}
>   
> +	if (flag == F2FS_GET_BLOCK_DIO && f2fs_lfs_mode(sbi)) {
> +		int segno = GET_SEGNO(sbi, blkaddr);
> +		bool last_seg, last_blk;
> +
> +		last_seg = !((segno + 1) % SEGS_PER_SEC(sbi));
> +		last_blk = (f2fs_usable_blks_in_seg(sbi, segno) - 1) ==
> +				GET_BLKOFF_FROM_SEG0(sbi, blkaddr);
> +
> +		/* LBA of the next block to be allocated may not be contiguous. */
> +		if (last_seg && last_blk)
> +			goto sync_out;
> +	}
> +
>   	if (pgofs >= end)
>   		goto sync_out;
>   	else if (dn.ofs_in_node < end_offset)



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