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Date:   Fri, 13 Aug 2021 15:00:55 +0200
From:   Jan Kara <jack@...e.cz>
To:     Zhang Yi <yi.zhang@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, jack@...e.cz, yukuai3@...wei.com
Subject: Re: [PATCH 2/3] ext4: remove an unnecessary if statement in
 __ext4_get_inode_loc()

On Tue 10-08-21 22:27:21, Zhang Yi wrote:
> The "if (!buffer_uptodate(bh))" hunk covered almost the whole code after
> getting buffer in __ext4_get_inode_loc() which seems unnecessary, remove
> it and switch to check ext4_buffer_uptodate(), it simplify code and make
> it more readable.
> 
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/inode.c | 162 +++++++++++++++++++++++-------------------------
>  1 file changed, 78 insertions(+), 84 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index eb2526a35254..eae1b2d0b550 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4330,99 +4330,93 @@ static int __ext4_get_inode_loc(struct super_block *sb, unsigned long ino,
>  	bh = sb_getblk(sb, block);
>  	if (unlikely(!bh))
>  		return -ENOMEM;
> -	if (!buffer_uptodate(bh)) {
> -		lock_buffer(bh);
> -
> -		if (ext4_buffer_uptodate(bh)) {
> -			/* someone brought it uptodate while we waited */
> -			unlock_buffer(bh);
> -			goto has_buffer;
> -		}
> +	if (ext4_buffer_uptodate(bh))
> +		goto has_buffer;
>  
> -		/*
> -		 * If we have all information of the inode in memory and this
> -		 * is the only valid inode in the block, we need not read the
> -		 * block.
> -		 */
> -		if (in_mem) {
> -			struct buffer_head *bitmap_bh;
> -			int i, start;
> +	lock_buffer(bh);
> +	/*
> +	 * If we have all information of the inode in memory and this
> +	 * is the only valid inode in the block, we need not read the
> +	 * block.
> +	 */
> +	if (in_mem) {
> +		struct buffer_head *bitmap_bh;
> +		int i, start;
>  
> -			start = inode_offset & ~(inodes_per_block - 1);
> +		start = inode_offset & ~(inodes_per_block - 1);
>  
> -			/* Is the inode bitmap in cache? */
> -			bitmap_bh = sb_getblk(sb, ext4_inode_bitmap(sb, gdp));
> -			if (unlikely(!bitmap_bh))
> -				goto make_io;
> +		/* Is the inode bitmap in cache? */
> +		bitmap_bh = sb_getblk(sb, ext4_inode_bitmap(sb, gdp));
> +		if (unlikely(!bitmap_bh))
> +			goto make_io;
>  
> -			/*
> -			 * If the inode bitmap isn't in cache then the
> -			 * optimisation may end up performing two reads instead
> -			 * of one, so skip it.
> -			 */
> -			if (!buffer_uptodate(bitmap_bh)) {
> -				brelse(bitmap_bh);
> -				goto make_io;
> -			}
> -			for (i = start; i < start + inodes_per_block; i++) {
> -				if (i == inode_offset)
> -					continue;
> -				if (ext4_test_bit(i, bitmap_bh->b_data))
> -					break;
> -			}
> +		/*
> +		 * If the inode bitmap isn't in cache then the
> +		 * optimisation may end up performing two reads instead
> +		 * of one, so skip it.
> +		 */
> +		if (!buffer_uptodate(bitmap_bh)) {
>  			brelse(bitmap_bh);
> -			if (i == start + inodes_per_block) {
> -				/* all other inodes are free, so skip I/O */
> -				memset(bh->b_data, 0, bh->b_size);
> -				set_buffer_uptodate(bh);
> -				unlock_buffer(bh);
> -				goto has_buffer;
> -			}
> +			goto make_io;
> +		}
> +		for (i = start; i < start + inodes_per_block; i++) {
> +			if (i == inode_offset)
> +				continue;
> +			if (ext4_test_bit(i, bitmap_bh->b_data))
> +				break;
>  		}
> +		brelse(bitmap_bh);
> +		if (i == start + inodes_per_block) {
> +			/* all other inodes are free, so skip I/O */
> +			memset(bh->b_data, 0, bh->b_size);
> +			set_buffer_uptodate(bh);
> +			unlock_buffer(bh);
> +			goto has_buffer;
> +		}
> +	}
>  
>  make_io:
> -		/*
> -		 * If we need to do any I/O, try to pre-readahead extra
> -		 * blocks from the inode table.
> -		 */
> -		blk_start_plug(&plug);
> -		if (EXT4_SB(sb)->s_inode_readahead_blks) {
> -			ext4_fsblk_t b, end, table;
> -			unsigned num;
> -			__u32 ra_blks = EXT4_SB(sb)->s_inode_readahead_blks;
> -
> -			table = ext4_inode_table(sb, gdp);
> -			/* s_inode_readahead_blks is always a power of 2 */
> -			b = block & ~((ext4_fsblk_t) ra_blks - 1);
> -			if (table > b)
> -				b = table;
> -			end = b + ra_blks;
> -			num = EXT4_INODES_PER_GROUP(sb);
> -			if (ext4_has_group_desc_csum(sb))
> -				num -= ext4_itable_unused_count(sb, gdp);
> -			table += num / inodes_per_block;
> -			if (end > table)
> -				end = table;
> -			while (b <= end)
> -				ext4_sb_breadahead_unmovable(sb, b++);
> -		}
> +	/*
> +	 * If we need to do any I/O, try to pre-readahead extra
> +	 * blocks from the inode table.
> +	 */
> +	blk_start_plug(&plug);
> +	if (EXT4_SB(sb)->s_inode_readahead_blks) {
> +		ext4_fsblk_t b, end, table;
> +		unsigned num;
> +		__u32 ra_blks = EXT4_SB(sb)->s_inode_readahead_blks;
> +
> +		table = ext4_inode_table(sb, gdp);
> +		/* s_inode_readahead_blks is always a power of 2 */
> +		b = block & ~((ext4_fsblk_t) ra_blks - 1);
> +		if (table > b)
> +			b = table;
> +		end = b + ra_blks;
> +		num = EXT4_INODES_PER_GROUP(sb);
> +		if (ext4_has_group_desc_csum(sb))
> +			num -= ext4_itable_unused_count(sb, gdp);
> +		table += num / inodes_per_block;
> +		if (end > table)
> +			end = table;
> +		while (b <= end)
> +			ext4_sb_breadahead_unmovable(sb, b++);
> +	}
>  
> -		/*
> -		 * There are other valid inodes in the buffer, this inode
> -		 * has in-inode xattrs, or we don't have this inode in memory.
> -		 * Read the block from disk.
> -		 */
> -		trace_ext4_load_inode(sb, ino);
> -		ext4_read_bh_nowait(bh, REQ_META | REQ_PRIO, NULL);
> -		blk_finish_plug(&plug);
> -		wait_on_buffer(bh);
> -		ext4_simulate_fail_bh(sb, bh, EXT4_SIM_INODE_EIO);
> -		if (!buffer_uptodate(bh)) {
> -			if (ret_block)
> -				*ret_block = block;
> -			brelse(bh);
> -			return -EIO;
> -		}
> +	/*
> +	 * There are other valid inodes in the buffer, this inode
> +	 * has in-inode xattrs, or we don't have this inode in memory.
> +	 * Read the block from disk.
> +	 */
> +	trace_ext4_load_inode(sb, ino);
> +	ext4_read_bh_nowait(bh, REQ_META | REQ_PRIO, NULL);
> +	blk_finish_plug(&plug);
> +	wait_on_buffer(bh);
> +	ext4_simulate_fail_bh(sb, bh, EXT4_SIM_INODE_EIO);
> +	if (!buffer_uptodate(bh)) {
> +		if (ret_block)
> +			*ret_block = block;
> +		brelse(bh);
> +		return -EIO;
>  	}
>  has_buffer:
>  	iloc->bh = bh;
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

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