ext4: make prefetch_block_bitmaps default

Block bitmap prefetching is needed for these allocator optimization
data structures to get populated and provide better group scanning
order. So, turn it on bu default. prefetch_block_bitmaps mount option
is now marked as removed and a new option no_prefetch_block_bitmaps is
added to disable block bitmap prefetching.

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20210401172129.189766-8-harshadshirwadkar@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -1227,7 +1227,7 @@ struct ext4_inode_info {
 #define EXT4_MOUNT_JOURNAL_CHECKSUM	0x800000 /* Journal checksums */
 #define EXT4_MOUNT_JOURNAL_ASYNC_COMMIT	0x1000000 /* Journal Async Commit */
 #define EXT4_MOUNT_WARN_ON_ERROR	0x2000000 /* Trigger WARN_ON on error */
-#define EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS 0x4000000
+#define EXT4_MOUNT_NO_PREFETCH_BLOCK_BITMAPS 0x4000000
 #define EXT4_MOUNT_DELALLOC		0x8000000 /* Delalloc support */
 #define EXT4_MOUNT_DATA_ERR_ABORT	0x10000000 /* Abort on file data write */
 #define EXT4_MOUNT_BLOCK_VALIDITY	0x20000000 /* Block validity checking */

fs/ext4/super.c

@@ -1688,7 +1688,7 @@ enum {
 	Opt_dioread_nolock, Opt_dioread_lock,
 	Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable,
 	Opt_max_dir_size_kb, Opt_nojournal_checksum, Opt_nombcache,
-	Opt_prefetch_block_bitmaps, Opt_mb_optimize_scan,
+	Opt_no_prefetch_block_bitmaps, Opt_mb_optimize_scan,
 #ifdef CONFIG_EXT4_DEBUG
 	Opt_fc_debug_max_replay, Opt_fc_debug_force
 #endif
@@ -1788,7 +1788,8 @@ static const match_table_t tokens = {
 	{Opt_inlinecrypt, "inlinecrypt"},
 	{Opt_nombcache, "nombcache"},
 	{Opt_nombcache, "no_mbcache"},	/* for backward compatibility */
-	{Opt_prefetch_block_bitmaps, "prefetch_block_bitmaps"},
+	{Opt_removed, "prefetch_block_bitmaps"},
+	{Opt_no_prefetch_block_bitmaps, "no_prefetch_block_bitmaps"},
 	{Opt_mb_optimize_scan, "mb_optimize_scan=%d"},
 	{Opt_removed, "check=none"},	/* mount option from ext2/3 */
 	{Opt_removed, "nocheck"},	/* mount option from ext2/3 */
@@ -2010,7 +2011,7 @@ static const struct mount_opts {
 	{Opt_max_dir_size_kb, 0, MOPT_GTE0},
 	{Opt_test_dummy_encryption, 0, MOPT_STRING},
 	{Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET},
-	{Opt_prefetch_block_bitmaps, EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS,
+	{Opt_no_prefetch_block_bitmaps, EXT4_MOUNT_NO_PREFETCH_BLOCK_BITMAPS,
 	 MOPT_SET},
 	{Opt_mb_optimize_scan, EXT4_MOUNT2_MB_OPTIMIZE_SCAN, MOPT_GTE0},
 #ifdef CONFIG_EXT4_DEBUG
@@ -3707,11 +3708,11 @@ static struct ext4_li_request *ext4_li_request_new(struct super_block *sb,
 
 	elr->lr_super = sb;
 	elr->lr_first_not_zeroed = start;
-	if (test_opt(sb, PREFETCH_BLOCK_BITMAPS))
-		elr->lr_mode = EXT4_LI_MODE_PREFETCH_BBITMAP;
-	else {
+	if (test_opt(sb, NO_PREFETCH_BLOCK_BITMAPS)) {
 		elr->lr_mode = EXT4_LI_MODE_ITABLE;
 		elr->lr_next_group = start;
+	} else {
+		elr->lr_mode = EXT4_LI_MODE_PREFETCH_BBITMAP;
 	}
 
 	/*
@@ -3742,7 +3743,7 @@ int ext4_register_li_request(struct super_block *sb,
 		goto out;
 	}
 
-	if (!test_opt(sb, PREFETCH_BLOCK_BITMAPS) &&
+	if (test_opt(sb, NO_PREFETCH_BLOCK_BITMAPS) &&
 	    (first_not_zeroed == ngroups || sb_rdonly(sb) ||
 	     !test_opt(sb, INIT_INODE_TABLE)))
 		goto out;