linux-ext4 - Re: [RFC v3 2/8] ext4: Refactor code related to freeing PAs

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Date:   Thu, 29 Sep 2022 13:26:13 +0200
From:   Jan Kara <jack@...e.cz>
To:     Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc:     linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>, rookxu <brookxu.cn@...il.com>,
        Ritesh Harjani <ritesh.list@...il.com>
Subject: Re: [RFC v3 2/8] ext4: Refactor code related to freeing PAs

On Tue 27-09-22 14:46:42, Ojaswin Mujoo wrote:
> This patch makes the following changes:
> 
> *  Rename ext4_mb_pa_free to ext4_mb_pa_put_free
>    to better reflect its purpose
> 
> *  Add new ext4_mb_pa_free() which only handles freeing
> 
> *  Refactor ext4_mb_pa_callback() to use ext4_mb_pa_free()
> 
> There are no functional changes in this patch
> 
> Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>

Looks good. Feel free to add:

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

								Honza

> ---
>  fs/ext4/mballoc.c | 29 ++++++++++++++++++++---------
>  1 file changed, 20 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 2e3eb632a216..8be6f8765a6f 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4531,16 +4531,21 @@ static void ext4_mb_mark_pa_deleted(struct super_block *sb,
>  	}
>  }
>  
> -static void ext4_mb_pa_callback(struct rcu_head *head)
> +static void inline ext4_mb_pa_free(struct ext4_prealloc_space *pa)
>  {
> -	struct ext4_prealloc_space *pa;
> -	pa = container_of(head, struct ext4_prealloc_space, u.pa_rcu);
> -
> +	BUG_ON(!pa);
>  	BUG_ON(atomic_read(&pa->pa_count));
>  	BUG_ON(pa->pa_deleted == 0);
>  	kmem_cache_free(ext4_pspace_cachep, pa);
>  }
>  
> +static void ext4_mb_pa_callback(struct rcu_head *head)
> +{
> +	struct ext4_prealloc_space *pa;
> +	pa = container_of(head, struct ext4_prealloc_space, u.pa_rcu);
> +	ext4_mb_pa_free(pa);
> +}
> +
>  /*
>   * drops a reference to preallocated space descriptor
>   * if this was the last reference and the space is consumed
> @@ -5067,14 +5072,20 @@ static int ext4_mb_pa_alloc(struct ext4_allocation_context *ac)
>  	return 0;
>  }
>  
> -static void ext4_mb_pa_free(struct ext4_allocation_context *ac)
> +static void ext4_mb_pa_put_free(struct ext4_allocation_context *ac)
>  {
>  	struct ext4_prealloc_space *pa = ac->ac_pa;
>  
>  	BUG_ON(!pa);
>  	ac->ac_pa = NULL;
>  	WARN_ON(!atomic_dec_and_test(&pa->pa_count));
> -	kmem_cache_free(ext4_pspace_cachep, pa);
> +	/*
> +	 * current function is only called due to an error or due to
> +	 * len of found blocks < len of requested blocks hence the PA has not
> +	 * been added to grp->bb_prealloc_list. So we don't need to lock it
> +	 */
> +	pa->pa_deleted = 1;
> +	ext4_mb_pa_free(pa);
>  }
>  
>  #ifdef CONFIG_EXT4_DEBUG
> @@ -5623,13 +5634,13 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
>  		 * So we have to free this pa here itself.
>  		 */
>  		if (*errp) {
> -			ext4_mb_pa_free(ac);
> +			ext4_mb_pa_put_free(ac);
>  			ext4_discard_allocated_blocks(ac);
>  			goto errout;
>  		}
>  		if (ac->ac_status == AC_STATUS_FOUND &&
>  			ac->ac_o_ex.fe_len >= ac->ac_f_ex.fe_len)
> -			ext4_mb_pa_free(ac);
> +			ext4_mb_pa_put_free(ac);
>  	}
>  	if (likely(ac->ac_status == AC_STATUS_FOUND)) {
>  		*errp = ext4_mb_mark_diskspace_used(ac, handle, reserv_clstrs);
> @@ -5648,7 +5659,7 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
>  		 * If block allocation fails then the pa allocated above
>  		 * needs to be freed here itself.
>  		 */
> -		ext4_mb_pa_free(ac);
> +		ext4_mb_pa_put_free(ac);
>  		*errp = -ENOSPC;
>  	}
>  
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR