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Date: Tue, 16 Jan 2024 09:02:53 +0800
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Subject: Re: [PATCH] ext4: clear EXT4_GROUP_INFO_WAS_TRIMMED_BIT even mount
 with discard
To: yangerkun <yangerkun@huaweicloud.com>, <tytso@mit.edu>,
	<adilger.kernel@dilger.ca>
CC: <boyu.mt@taobao.com>, <linux-ext4@vger.kernel.org>
References: <20231230070654.178638-1-yangerkun@huaweicloud.com>
From: yangerkun <yangerkun@huawei.com>
In-Reply-To: <20231230070654.178638-1-yangerkun@huaweicloud.com>
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Ping...

在 2023/12/30 15:06, yangerkun 写道:
> Commit 3d56b8d2c74c ("ext4: Speed up FITRIM by recording flags in
> ext4_group_info") speed up fstrim by skipping trim trimmed group. We
> also has the chance to clear trimmed once there exists some block free
> for this group(mount without discard), and the next trim for this group
> will work well too.
> 
> For mount with discard, we will issue dicard when we free blocks, so
> leave trimmed flag keep alive to skip useless trim trigger from
> userspace seems reasonable. But for some case like ext4 build on
> dm-thinpool(ext4 blocksize 4K, pool blocksize 128K), discard from ext4
> maybe unaligned for dm thinpool, and thinpool will just finish this
> discard(see process_discard_bio when begein equals to end) without
> actually process discard. For this case, trim from userspace can really
> help us to free some thinpool block.
> 
> So convert to clear trimmed flag for all case no matter mounted with
> discard or not.
> 
> Fixes: 3d56b8d2c74c ("ext4: Speed up FITRIM by recording flags in ext4_group_info")
> Signed-off-by: yangerkun <yangerkun@huaweicloud.com>
> ---
>   fs/ext4/mballoc.c | 10 ++++------
>   1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index d72b5e3c92ec..69240ae775f1 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -3855,11 +3855,8 @@ static void ext4_free_data_in_buddy(struct super_block *sb,
>   	/*
>   	 * Clear the trimmed flag for the group so that the next
>   	 * ext4_trim_fs can trim it.
> -	 * If the volume is mounted with -o discard, online discard
> -	 * is supported and the free blocks will be trimmed online.
>   	 */
> -	if (!test_opt(sb, DISCARD))
> -		EXT4_MB_GRP_CLEAR_TRIMMED(db);
> +	EXT4_MB_GRP_CLEAR_TRIMMED(db);
>   
>   	if (!db->bb_free_root.rb_node) {
>   		/* No more items in the per group rb tree
> @@ -6481,8 +6478,9 @@ static void ext4_mb_clear_bb(handle_t *handle, struct inode *inode,
>   					 " group:%u block:%d count:%lu failed"
>   					 " with %d", block_group, bit, count,
>   					 err);
> -		} else
> -			EXT4_MB_GRP_CLEAR_TRIMMED(e4b.bd_info);
> +		}
> +
> +		EXT4_MB_GRP_CLEAR_TRIMMED(e4b.bd_info);
>   
>   		ext4_lock_group(sb, block_group);
>   		mb_free_blocks(inode, &e4b, bit, count_clusters);