ext4: change s_last_trim_minblks type to unsigned long

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>
Link: https://lore.kernel.org/r/20211103145122.17338-1-lczerner@redhat.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: Lukas Czerner

fs/ext4/ext4.h

@@ -1663,7 +1663,7 @@ 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;

fs/ext4/mballoc.c

@@ -6369,7 +6369,7 @@ 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);
@@ -6478,7 +6478,7 @@ 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;