linux-ext4 - [PATCH 1/2] ext4: Make mb_optimize_scan option work with set/unset mount cmd

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Date:   Tue,  8 Mar 2022 15:22:00 +0530
From:   Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To:     linux-ext4@...r.kernel.org
Cc:     Harshad Shirwadkar <harshadshirwadkar@...il.com>,
        "Theodore Ts'o" <tytso@....edu>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] ext4: Make mb_optimize_scan option work with set/unset mount cmd

After moving to the new mount API, mb_optimize_scan mount option
handling was not working as expected due to the parsed value always
being overwritten by default. Refactor and fix this to the expected
behavior described below:

*  mb_optimize_scan=1 - On
*  mb_optimize_scan=0 - Off
*  mb_optimize_scan not passed - On if no. of BGs > threshold else off
*  Remounts retain previous value unless we explicitly pass the option
   with a new value

Reported-by: Ritesh Harjani <riteshh@...ux.ibm.com>
Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
---
 fs/ext4/super.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index c5021ca0a28a..cd0547fabd79 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2021,12 +2021,12 @@ static int ext4_set_test_dummy_encryption(struct super_block *sb, char *arg)
 #define EXT4_SPEC_s_commit_interval		(1 << 16)
 #define EXT4_SPEC_s_fc_debug_max_replay		(1 << 17)
 #define EXT4_SPEC_s_sb_block			(1 << 18)
+#define EXT4_SPEC_mb_optimize_scan		(1 << 19)
 
 struct ext4_fs_context {
 	char		*s_qf_names[EXT4_MAXQUOTAS];
 	char		*test_dummy_enc_arg;
 	int		s_jquota_fmt;	/* Format of quota to use */
-	int		mb_optimize_scan;
 #ifdef CONFIG_EXT4_DEBUG
 	int s_fc_debug_max_replay;
 #endif
@@ -2451,12 +2451,17 @@ static int ext4_parse_param(struct fs_context *fc, struct fs_parameter *param)
 			ctx_clear_mount_opt(ctx, m->mount_opt);
 		return 0;
 	case Opt_mb_optimize_scan:
-		if (result.int_32 != 0 && result.int_32 != 1) {
+		if (result.int_32 == 1) {
+			ctx_set_mount_opt2(ctx, EXT4_MOUNT2_MB_OPTIMIZE_SCAN);
+			ctx->spec |= EXT4_SPEC_mb_optimize_scan;
+		} else if (result.int_32 == 0) {
+			ctx_clear_mount_opt2(ctx, EXT4_MOUNT2_MB_OPTIMIZE_SCAN);
+			ctx->spec |= EXT4_SPEC_mb_optimize_scan;
+		} else {
 			ext4_msg(NULL, KERN_WARNING,
 				 "mb_optimize_scan should be set to 0 or 1.");
 			return -EINVAL;
 		}
-		ctx->mb_optimize_scan = result.int_32;
 		return 0;
 	}
 
@@ -4369,7 +4374,6 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 
 	/* Set defaults for the variables that will be set during parsing */
 	ctx->journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
-	ctx->mb_optimize_scan = DEFAULT_MB_OPTIMIZE_SCAN;
 
 	sbi->s_inode_readahead_blks = EXT4_DEF_INODE_READAHEAD_BLKS;
 	sbi->s_sectors_written_start =
@@ -5320,12 +5324,12 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 	 * turned off by passing "mb_optimize_scan=0". This can also be
 	 * turned on forcefully by passing "mb_optimize_scan=1".
 	 */
-	if (ctx->mb_optimize_scan == 1)
-		set_opt2(sb, MB_OPTIMIZE_SCAN);
-	else if (ctx->mb_optimize_scan == 0)
-		clear_opt2(sb, MB_OPTIMIZE_SCAN);
-	else if (sbi->s_groups_count >= MB_DEFAULT_LINEAR_SCAN_THRESHOLD)
-		set_opt2(sb, MB_OPTIMIZE_SCAN);
+	if (!(ctx->spec & EXT4_SPEC_mb_optimize_scan)) {
+		if (sbi->s_groups_count >= MB_DEFAULT_LINEAR_SCAN_THRESHOLD)
+			set_opt2(sb, MB_OPTIMIZE_SCAN);
+		else
+			clear_opt2(sb, MB_OPTIMIZE_SCAN);
+	}
 
 	err = ext4_mb_init(sb);
 	if (err) {
-- 
2.27.0