linux-ext4 - Re: [PATCH v7 02/12] ext4: factor out codes to update block bitmap and group descriptor on disk from ext4_mb_mark

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Message-Id: <87zg18f1bm.fsf@doe.com>
Date:   Wed, 27 Sep 2023 14:19:17 +0530
From:   Ritesh Harjani (IBM) <ritesh.list@...il.com>
To:     Kemeng Shi <shikemeng@...weicloud.com>, tytso@....edu,
        adilger.kernel@...ger.ca
Cc:     ojaswin@...ux.ibm.com, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 02/12] ext4: factor out codes to update block bitmap and group descriptor on disk from ext4_mb_mark_bb

Kemeng Shi <shikemeng@...weicloud.com> writes:

> There are several reasons to add a general function ext4_mb_mark_context
> to update block bitmap and group descriptor on disk:
> 1. pair behavior of alloc/free bits. For example,
> ext4_mb_new_blocks_simple will update free_clusters in struct flex_groups
> in ext4_mb_mark_bb while ext4_free_blocks_simple forgets this.
> 2. remove repeat code to read from disk, update and write back to disk.
> 3. reduce future unit test mocks to catch real IO to update structure
> on disk.
>
> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
> ---
>  fs/ext4/mballoc.c | 147 ++++++++++++++++++++++++----------------------
>  1 file changed, 77 insertions(+), 70 deletions(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index cf09adfbaf11..e1320eea46e9 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -3953,6 +3953,80 @@ void ext4_exit_mballoc(void)
>  	ext4_groupinfo_destroy_slabs();
>  }
>  
> +static int
> +ext4_mb_mark_context(struct super_block *sb, bool state, ext4_group_t group,
> +		     ext4_grpblk_t blkoff, ext4_grpblk_t len)


ext4_grpblk_t is defined as int.
    /* data type for block offset of block group */
    typedef int ext4_grpblk_t;

I think len should be unsigned int (u32) here. 

> +{
> +	struct ext4_sb_info *sbi = EXT4_SB(sb);
> +	struct buffer_head *bitmap_bh = NULL;
> +	struct ext4_group_desc *gdp;
> +	struct buffer_head *gdp_bh;
> +	int err;
> +	unsigned int i, already, changed;
> +
> +	bitmap_bh = ext4_read_block_bitmap(sb, group);
> +	if (IS_ERR(bitmap_bh))
> +		return PTR_ERR(bitmap_bh);
> +
> +	err = -EIO;
> +	gdp = ext4_get_group_desc(sb, group, &gdp_bh);
> +	if (!gdp)
> +		goto out_err;
> +
> +	ext4_lock_group(sb, group);
> +	if (ext4_has_group_desc_csum(sb) &&
> +	    (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))) {
> +		gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
> +		ext4_free_group_clusters_set(sb, gdp,
> +			ext4_free_clusters_after_init(sb, group, gdp));
> +	}
> +
> +	already = 0;
> +	for (i = 0; i < len; i++)
> +		if (mb_test_bit(blkoff + i, bitmap_bh->b_data) ==
> +				state)
> +			already++;
> +	changed = len - already;
> +
> +	if (state) {
> +		mb_set_bits(bitmap_bh->b_data, blkoff, len);
> +		ext4_free_group_clusters_set(sb, gdp,
> +			ext4_free_group_clusters(sb, gdp) - changed);
> +	} else {
> +		mb_clear_bits(bitmap_bh->b_data, blkoff, len);
> +		ext4_free_group_clusters_set(sb, gdp,
> +			ext4_free_group_clusters(sb, gdp) + changed);
> +	}
> +
> +	ext4_block_bitmap_csum_set(sb, gdp, bitmap_bh);
> +	ext4_group_desc_csum_set(sb, group, gdp);
> +	ext4_unlock_group(sb, group);
> +
> +	if (sbi->s_log_groups_per_flex) {
> +		ext4_group_t flex_group = ext4_flex_group(sbi, group);
> +		struct flex_groups *fg = sbi_array_rcu_deref(sbi,
> +					   s_flex_groups, flex_group);
> +
> +		if (state)
> +			atomic64_sub(changed, &fg->free_clusters);
> +		else
> +			atomic64_add(changed, &fg->free_clusters);
> +	}
> +
> +	err = ext4_handle_dirty_metadata(NULL, NULL, bitmap_bh);
> +	if (err)
> +		goto out_err;
> +	err = ext4_handle_dirty_metadata(NULL, NULL, gdp_bh);
> +	if (err)
> +		goto out_err;
> +
> +	sync_dirty_buffer(bitmap_bh);
> +	sync_dirty_buffer(gdp_bh);
> +
> +out_err:
> +	brelse(bitmap_bh);
> +	return err;
> +}
>  
>  /*
>   * Check quota and mark chosen space (ac->ac_b_ex) non-free in bitmaps
> @@ -4079,15 +4153,11 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
>  void ext4_mb_mark_bb(struct super_block *sb, ext4_fsblk_t block,
>  		     int len, bool state)

Even ext4_mb_mark_bb should take len as unsigned int IMO.
For e.g. ext4_fc_replay_add_range() passes map.m_len which is also
unsigned int.


Otherwise the patch looks good to me. Feel free to add - 

Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>

-ritesh