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Date: Mon, 3 Jun 2024 16:07:05 +0200
From: Jan Kara <jack@suse.cz>
To: Junchao Sun <sunjunchao2870@gmail.com>
Cc: linux-ext4@vger.kernel.org, tytso@mit.edu, adilger.kernel@dilger.ca,
	jack@suse.cz
Subject: Re: [PATCH] ext4: Adjust the layout of the ext4_inode_info structure
 to save memory.
Message-ID: <20240603140705.vfpdrbyljw6yfxpd@quack3>
References: <20240603131524.324224-1-sunjunchao2870@gmail.com>
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In-Reply-To: <20240603131524.324224-1-sunjunchao2870@gmail.com>

On Mon 03-06-24 21:15:24, Junchao Sun wrote:
> Using pahole, we can see that there are some padding holes
> in the current ext4_inode_info structure. Adjusting the
> layout of ext4_inode_info can reduce these holes,
> resulting in the size of the structure decreasing
> from 2424 bytes to 2408 bytes.

But AFAICT this will save two holes 4 bytes each so only 8 bytes in total?
Not 16?

> 
> Signed-off-by: Junchao Sun <sunjunchao2870@gmail.com>

Otherwise looks good. Feel free to add:

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

								Honza

> ---
>  fs/ext4/ext4.h | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 023571f8dd1b..42bcd4f749a8 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1055,6 +1055,7 @@ struct ext4_inode_info {
>  
>  	/* Number of ongoing updates on this inode */
>  	atomic_t  i_fc_updates;
> +	atomic_t i_unwritten; /* Nr. of inflight conversions pending */
>  
>  	/* Fast commit wait queue for this inode */
>  	wait_queue_head_t i_fc_wait;
> @@ -1103,6 +1104,10 @@ struct ext4_inode_info {
>  
>  	/* mballoc */
>  	atomic_t i_prealloc_active;
> +
> +	/* allocation reservation info for delalloc */
> +	/* In case of bigalloc, this refer to clusters rather than blocks */
> +	unsigned int i_reserved_data_blocks;
>  	struct rb_root i_prealloc_node;
>  	rwlock_t i_prealloc_lock;
>  
> @@ -1119,10 +1124,6 @@ struct ext4_inode_info {
>  	/* ialloc */
>  	ext4_group_t	i_last_alloc_group;
>  
> -	/* allocation reservation info for delalloc */
> -	/* In case of bigalloc, this refer to clusters rather than blocks */
> -	unsigned int i_reserved_data_blocks;
> -
>  	/* pending cluster reservations for bigalloc file systems */
>  	struct ext4_pending_tree i_pending_tree;
>  
> @@ -1146,7 +1147,6 @@ struct ext4_inode_info {
>  	 */
>  	struct list_head i_rsv_conversion_list;
>  	struct work_struct i_rsv_conversion_work;
> -	atomic_t i_unwritten; /* Nr. of inflight conversions pending */
>  
>  	spinlock_t i_block_reservation_lock;
>  
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR