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Date: Tue, 23 Apr 2024 23:46:51 +0200
From: Jan Kara <jack@suse.cz>
To: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: tytso@mit.edu, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org,
	linux-kernel@vger.kernel.org, jack@suse.cz, ojaswin@linux.ibm.com,
	ritesh.list@gmail.com
Subject: Re: [PATCH v2 5/5] ext4: open coding repeated check in
 next_linear_group
Message-ID: <20240423214651.v7veh2x2pmkpxti4@quack3>
References: <20240423124046.974134-1-shikemeng@huaweicloud.com>
 <20240423124046.974134-6-shikemeng@huaweicloud.com>
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In-Reply-To: <20240423124046.974134-6-shikemeng@huaweicloud.com>

On Tue 23-04-24 20:40:46, Kemeng Shi wrote:
> Open coding repeated check in next_linear_group.
> 
> Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>

Looks good. Feel free to add:

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

								Honza

> ---
>  fs/ext4/mballoc.c | 31 +++++++++++++++----------------
>  1 file changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 71b2f9a18875..4afe5bb94bf4 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -1076,23 +1076,11 @@ static inline int should_optimize_scan(struct ext4_allocation_context *ac)
>  }
>  
>  /*
> - * Return next linear group for allocation. If linear traversal should not be
> - * performed, this function just returns the same group
> + * Return next linear group for allocation.
>   */
>  static ext4_group_t
> -next_linear_group(struct ext4_allocation_context *ac, ext4_group_t group,
> -		  ext4_group_t ngroups)
> +next_linear_group(ext4_group_t group, ext4_group_t ngroups)
>  {
> -	if (!should_optimize_scan(ac))
> -		goto inc_and_return;
> -
> -	if (ac->ac_groups_linear_remaining) {
> -		ac->ac_groups_linear_remaining--;
> -		goto inc_and_return;
> -	}
> -
> -	return group;
> -inc_and_return:
>  	/*
>  	 * Artificially restricted ngroups for non-extent
>  	 * files makes group > ngroups possible on first loop.
> @@ -1118,8 +1106,19 @@ static void ext4_mb_choose_next_group(struct ext4_allocation_context *ac,
>  {
>  	*new_cr = ac->ac_criteria;
>  
> -	if (!should_optimize_scan(ac) || ac->ac_groups_linear_remaining) {
> -		*group = next_linear_group(ac, *group, ngroups);
> +	if (!should_optimize_scan(ac)) {
> +		*group = next_linear_group(*group, ngroups);
> +		return;
> +	}
> +
> +	/*
> +	 * Optimized scanning can return non adjacent groups which can cause
> +	 * seek overhead for rotational disks. So try few linear groups before
> +	 * trying optimized scan.
> +	 */
> +	if (ac->ac_groups_linear_remaining) {
> +		*group = next_linear_group(*group, ngroups);
> +		ac->ac_groups_linear_remaining--;
>  		return;
>  	}
>  
> -- 
> 2.30.0
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR