Re: [PATCH 1/2] ext4: Change s_last_trim_minblks type to unsigned long

From: Andreas Dilger <adilger@dilger.ca>
To: Lukas Czerner <lczerner@redhat.com>
Cc: linux-ext4@vger.kernel.org, tytso@mit.edu
Subject: Re: [PATCH 1/2] ext4: Change s_last_trim_minblks type to unsigned long
Date: Wed, 3 Nov 2021 14:20:05 -0600	[thread overview]
Message-ID: <BEFE9A1D-A336-4C19-9B9A-5343EC3D4364@dilger.ca> (raw)
In-Reply-To: <20211103145122.17338-1-lczerner@redhat.com>

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On Nov 3, 2021, at 8:51 AM, Lukas Czerner <lczerner@redhat.com> wrote:
> 
> There is no good reason for the s_last_trim_minblks to be atomic. There is
> no data integrity needed and there is no real danger in setting and
> reading it in a racy manner. Change it to be unsigned long, the same type
> as s_clusters_per_group which is the maximum that's allowed.
> 
> Signed-off-by: Lukas Czerner <lczerner@redhat.com>
> Suggested-by: Andreas Dilger <adilger@dilger.ca>

Reviewed-by: Andreas Dilger <adilger@dilger.ca>

Could also add for reference:

Fixes: 3d56b8d2c74c ("ext4: Speed up FITRIM by recording flags in ext4_group_info")

> ---
> fs/ext4/ext4.h    | 2 +-
> fs/ext4/mballoc.c | 4 ++--
> 2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 3825195539d7..92a155401f61 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1660,7 +1660,7 @@ struct ext4_sb_info {
> 	struct task_struct *s_mmp_tsk;
> 
> 	/* record the last minlen when FITRIM is called. */
> -	atomic_t s_last_trim_minblks;
> +	unsigned long s_last_trim_minblks;
> 
> 	/* Reference to checksum algorithm driver via cryptoapi */
> 	struct crypto_shash *s_chksum_driver;
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 72bfac2d6dce..eda550ec3956 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -6374,7 +6374,7 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
> 	ext4_lock_group(sb, group);
> 
> 	if (!EXT4_MB_GRP_WAS_TRIMMED(e4b.bd_info) ||
> -	    minblocks < atomic_read(&EXT4_SB(sb)->s_last_trim_minblks)) {
> +	    minblocks < EXT4_SB(sb)->s_last_trim_minblks) {
> 		ret = ext4_try_to_trim_range(sb, &e4b, start, max, minblocks);
> 		if (ret >= 0)
> 			EXT4_MB_GRP_SET_TRIMMED(e4b.bd_info);
> @@ -6475,7 +6475,7 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
> 	}
> 
> 	if (!ret)
> -		atomic_set(&EXT4_SB(sb)->s_last_trim_minblks, minlen);
> +		EXT4_SB(sb)->s_last_trim_minblks = minlen;
> 
> out:
> 	range->len = EXT4_C2B(EXT4_SB(sb), trimmed) << sb->s_blocksize_bits;
> --
> 2.31.1
> 

Cheers, Andreas

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