[PATCH 1/2] ext4: make trim/discard optional (and off by default)

[PATCH 1/2] ext4: make trim/discard optional (and off by default)

[Eric Sandeen]

It is anticipated that when sb_issue_discard starts doing
real work on trim-capable devices, we may see issues.  Make
this mount-time optional, and default it to off until we know
that things are working out OK.

(Q: should we call this "discard" instead?  What's the more common
term users might expect ... ?)

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
---


diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 6d94e06..87036af 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -353,6 +353,12 @@ noauto_da_alloc		replacing existing files via patterns such as
 			system crashes before the delayed allocation
 			blocks are forced to disk.
 
+trim			Controls whether ext4 should issue TRIM/discard
+notrim(*)		commands to the underlying block device when
+			blocks are freed.  This is useful for SSD devices
+			and sparse/thinly-provisioned LUNs, but it is off
+			by default until sufficient testing has been done.
+
 Data Mode
 =========
 There are 3 different data modes:
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 8825515..410adb6 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -750,6 +750,7 @@ struct ext4_inode_info {
 #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 */
+#define EXT4_MOUNT_TRIM			0x40000000 /* Issue TRIM requests */
 
 #define clear_opt(o, opt)		o &= ~EXT4_MOUNT_##opt
 #define set_opt(o, opt)			o |= EXT4_MOUNT_##opt
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index bba1282..8a4f77b 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2529,7 +2529,6 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
 	struct ext4_group_info *db;
 	int err, count = 0, count2 = 0;
 	struct ext4_free_data *entry;
-	ext4_fsblk_t discard_block;
 	struct list_head *l, *ltmp;
 
 	list_for_each_safe(l, ltmp, &txn->t_private_list) {
@@ -2559,13 +2558,19 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
 			page_cache_release(e4b.bd_bitmap_page);
 		}
 		ext4_unlock_group(sb, entry->group);
-		discard_block = (ext4_fsblk_t) entry->group * EXT4_BLOCKS_PER_GROUP(sb)
-			+ entry->start_blk
-			+ le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
-		trace_ext4_discard_blocks(sb, (unsigned long long)discard_block,
-					  entry->count);
-		sb_issue_discard(sb, discard_block, entry->count);
-
+		if (test_opt(sb, TRIM)) {
+			ext4_fsblk_t discard_block;
+			struct ext4_super_block *es = EXT4_SB(sb)->s_es;
+
+			discard_block = (ext4_fsblk_t)entry->group *
+						EXT4_BLOCKS_PER_GROUP(sb)
+					+ entry->start_blk
+					+ le32_to_cpu(es->s_first_data_block);
+			trace_ext4_discard_blocks(sb,
+					(unsigned long long)discard_block,
+					entry->count);
+			sb_issue_discard(sb, discard_block, entry->count);
+		}
 		kmem_cache_free(ext4_free_ext_cachep, entry);
 		ext4_mb_release_desc(&e4b);
 	}
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d4ca92a..fc4a8d8 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -899,6 +899,9 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
 	if (test_opt(sb, NO_AUTO_DA_ALLOC))
 		seq_puts(seq, ",noauto_da_alloc");
 
+	if (test_opt(sb, TRIM))
+		seq_puts(seq, ",trim");
+
 	ext4_show_quota_options(seq, sb);
 
 	return 0;
@@ -1079,7 +1082,8 @@ enum {
 	Opt_usrquota, Opt_grpquota, Opt_i_version,
 	Opt_stripe, Opt_delalloc, Opt_nodelalloc,
 	Opt_block_validity, Opt_noblock_validity,
-	Opt_inode_readahead_blks, Opt_journal_ioprio
+	Opt_inode_readahead_blks, Opt_journal_ioprio,
+	Opt_trim, Opt_notrim,
 };
 
 static const match_table_t tokens = {
@@ -1144,6 +1148,8 @@ static const match_table_t tokens = {
 	{Opt_auto_da_alloc, "auto_da_alloc=%u"},
 	{Opt_auto_da_alloc, "auto_da_alloc"},
 	{Opt_noauto_da_alloc, "noauto_da_alloc"},
+	{Opt_trim, "trim"},
+	{Opt_notrim, "notrim"},
 	{Opt_err, NULL},
 };
 
@@ -1565,6 +1571,12 @@ set_qf_format:
 			else
 				set_opt(sbi->s_mount_opt,NO_AUTO_DA_ALLOC);
 			break;
+		case Opt_trim:
+			set_opt(sbi->s_mount_opt, TRIM);
+			break;
+		case Opt_notrim:
+			clear_opt(sbi->s_mount_opt, TRIM);
+			break;
 		default:
 			ext4_msg(sb, KERN_ERR,
 			       "Unrecognized mount option \"%s\" "

Re: [PATCH 1/2] ext4: make trim/discard optional (and off by default)

[Ric Wheeler]

On 11/16/2009 05:44 PM, Eric Sandeen wrote:
> It is anticipated that when sb_issue_discard starts doing
> real work on trim-capable devices, we may see issues.  Make
> this mount-time optional, and default it to off until we know
> that things are working out OK.
>
> (Q: should we call this "discard" instead?  What's the more common
> term users might expect ... ?)

Users will be confused regardless of what we do here, but the actual 
discard only invokes ATA_TRIM commands on ATA devices. (SCSI uses its 
own command, either a WRITE_SAME with discard or UNMAP).

Not sure that any real user cares since they both end up doing roughly 
the same thing...

ric

>
> Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
> ---
>
>
> diff --git a/Documentation/filesystems/ext4.txt 
> b/Documentation/filesystems/ext4.txt
> index 6d94e06..87036af 100644
> --- a/Documentation/filesystems/ext4.txt
> +++ b/Documentation/filesystems/ext4.txt
> @@ -353,6 +353,12 @@ noauto_da_alloc        replacing existing files 
> via patterns such as
>             system crashes before the delayed allocation
>             blocks are forced to disk.
>
> +trim            Controls whether ext4 should issue TRIM/discard
> +notrim(*)        commands to the underlying block device when
> +            blocks are freed.  This is useful for SSD devices
> +            and sparse/thinly-provisioned LUNs, but it is off
> +            by default until sufficient testing has been done.
> +
> Data Mode
> =========
> There are 3 different data modes:
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 8825515..410adb6 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -750,6 +750,7 @@ struct ext4_inode_info {
> #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 */
> +#define EXT4_MOUNT_TRIM            0x40000000 /* Issue TRIM requests */
>
> #define clear_opt(o, opt)        o &= ~EXT4_MOUNT_##opt
> #define set_opt(o, opt)            o |= EXT4_MOUNT_##opt
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index bba1282..8a4f77b 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2529,7 +2529,6 @@ static void release_blocks_on_commit(journal_t 
> *journal, transaction_t *txn)
>     struct ext4_group_info *db;
>     int err, count = 0, count2 = 0;
>     struct ext4_free_data *entry;
> -    ext4_fsblk_t discard_block;
>     struct list_head *l, *ltmp;
>
>     list_for_each_safe(l, ltmp, &txn->t_private_list) {
> @@ -2559,13 +2558,19 @@ static void release_blocks_on_commit(journal_t 
> *journal, transaction_t *txn)
>             page_cache_release(e4b.bd_bitmap_page);
>         }
>         ext4_unlock_group(sb, entry->group);
> -        discard_block = (ext4_fsblk_t) entry->group * 
> EXT4_BLOCKS_PER_GROUP(sb)
> -            + entry->start_blk
> -            + le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
> -        trace_ext4_discard_blocks(sb, (unsigned long long)discard_block,
> -                      entry->count);
> -        sb_issue_discard(sb, discard_block, entry->count);
> -
> +        if (test_opt(sb, TRIM)) {
> +            ext4_fsblk_t discard_block;
> +            struct ext4_super_block *es = EXT4_SB(sb)->s_es;
> +
> +            discard_block = (ext4_fsblk_t)entry->group *
> +                        EXT4_BLOCKS_PER_GROUP(sb)
> +                    + entry->start_blk
> +                    + le32_to_cpu(es->s_first_data_block);
> +            trace_ext4_discard_blocks(sb,
> +                    (unsigned long long)discard_block,
> +                    entry->count);
> +            sb_issue_discard(sb, discard_block, entry->count);
> +        }
>         kmem_cache_free(ext4_free_ext_cachep, entry);
>         ext4_mb_release_desc(&e4b);
>     }
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index d4ca92a..fc4a8d8 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -899,6 +899,9 @@ static int ext4_show_options(struct seq_file *seq, 
> struct vfsmount *vfs)
>     if (test_opt(sb, NO_AUTO_DA_ALLOC))
>         seq_puts(seq, ",noauto_da_alloc");
>
> +    if (test_opt(sb, TRIM))
> +        seq_puts(seq, ",trim");
> +
>     ext4_show_quota_options(seq, sb);
>
>     return 0;
> @@ -1079,7 +1082,8 @@ enum {
>     Opt_usrquota, Opt_grpquota, Opt_i_version,
>     Opt_stripe, Opt_delalloc, Opt_nodelalloc,
>     Opt_block_validity, Opt_noblock_validity,
> -    Opt_inode_readahead_blks, Opt_journal_ioprio
> +    Opt_inode_readahead_blks, Opt_journal_ioprio,
> +    Opt_trim, Opt_notrim,
> };
>
> static const match_table_t tokens = {
> @@ -1144,6 +1148,8 @@ static const match_table_t tokens = {
>     {Opt_auto_da_alloc, "auto_da_alloc=%u"},
>     {Opt_auto_da_alloc, "auto_da_alloc"},
>     {Opt_noauto_da_alloc, "noauto_da_alloc"},
> +    {Opt_trim, "trim"},
> +    {Opt_notrim, "notrim"},
>     {Opt_err, NULL},
> };
>
> @@ -1565,6 +1571,12 @@ set_qf_format:
>             else
>                 set_opt(sbi->s_mount_opt,NO_AUTO_DA_ALLOC);
>             break;
> +        case Opt_trim:
> +            set_opt(sbi->s_mount_opt, TRIM);
> +            break;
> +        case Opt_notrim:
> +            clear_opt(sbi->s_mount_opt, TRIM);
> +            break;
>         default:
>             ext4_msg(sb, KERN_ERR,
>                    "Unrecognized mount option \"%s\" "
>
> -- 
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> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

[PATCH 1/2 V2] ext4: make trim/discard optional (and off by default)

[Eric Sandeen]

It is anticipated that when sb_issue_discard starts doing
real work on trim-capable devices, we may see issues.  Make
this mount-time optional, and default it to off until we know
that things are working out OK.

V2: rename "trim" to "discard" to match btrfs & gfs2

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
---

diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 6d94e06..26904ff 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -353,6 +353,12 @@ noauto_da_alloc		replacing existing files via patterns such as
 			system crashes before the delayed allocation
 			blocks are forced to disk.
 
+discard		Controls whether ext4 should issue discard/TRIM
+nodiscard(*)		commands to the underlying block device when
+			blocks are freed.  This is useful for SSD devices
+			and sparse/thinly-provisioned LUNs, but it is off
+			by default until sufficient testing has been done.
+
 Data Mode
 =========
 There are 3 different data modes:
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 8825515..05ce38b 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -750,6 +750,7 @@ struct ext4_inode_info {
 #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 */
+#define EXT4_MOUNT_DISCARD		0x40000000 /* Issue DISCARD requests */
 
 #define clear_opt(o, opt)		o &= ~EXT4_MOUNT_##opt
 #define set_opt(o, opt)			o |= EXT4_MOUNT_##opt
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index bba1282..6e5a23a 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2529,7 +2529,6 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
 	struct ext4_group_info *db;
 	int err, count = 0, count2 = 0;
 	struct ext4_free_data *entry;
-	ext4_fsblk_t discard_block;
 	struct list_head *l, *ltmp;
 
 	list_for_each_safe(l, ltmp, &txn->t_private_list) {
@@ -2559,13 +2558,19 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
 			page_cache_release(e4b.bd_bitmap_page);
 		}
 		ext4_unlock_group(sb, entry->group);
-		discard_block = (ext4_fsblk_t) entry->group * EXT4_BLOCKS_PER_GROUP(sb)
-			+ entry->start_blk
-			+ le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
-		trace_ext4_discard_blocks(sb, (unsigned long long)discard_block,
-					  entry->count);
-		sb_issue_discard(sb, discard_block, entry->count);
-
+		if (test_opt(sb, DISCARD)) {
+			ext4_fsblk_t discard_block;
+			struct ext4_super_block *es = EXT4_SB(sb)->s_es;
+
+			discard_block = (ext4_fsblk_t)entry->group *
+						EXT4_BLOCKS_PER_GROUP(sb)
+					+ entry->start_blk
+					+ le32_to_cpu(es->s_first_data_block);
+			trace_ext4_discard_blocks(sb,
+					(unsigned long long)discard_block,
+					entry->count);
+			sb_issue_discard(sb, discard_block, entry->count);
+		}
 		kmem_cache_free(ext4_free_ext_cachep, entry);
 		ext4_mb_release_desc(&e4b);
 	}
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d4ca92a..b9638d9 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -899,6 +899,9 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
 	if (test_opt(sb, NO_AUTO_DA_ALLOC))
 		seq_puts(seq, ",noauto_da_alloc");
 
+	if (test_opt(sb, DISCARD))
+		seq_puts(seq, ",discard");
+
 	ext4_show_quota_options(seq, sb);
 
 	return 0;
@@ -1079,7 +1082,8 @@ enum {
 	Opt_usrquota, Opt_grpquota, Opt_i_version,
 	Opt_stripe, Opt_delalloc, Opt_nodelalloc,
 	Opt_block_validity, Opt_noblock_validity,
-	Opt_inode_readahead_blks, Opt_journal_ioprio
+	Opt_inode_readahead_blks, Opt_journal_ioprio,
+	Opt_discard, Opt_nodiscard,
 };
 
 static const match_table_t tokens = {
@@ -1144,6 +1148,8 @@ static const match_table_t tokens = {
 	{Opt_auto_da_alloc, "auto_da_alloc=%u"},
 	{Opt_auto_da_alloc, "auto_da_alloc"},
 	{Opt_noauto_da_alloc, "noauto_da_alloc"},
+	{Opt_discard, "discard"},
+	{Opt_nodiscard, "nodiscard"},
 	{Opt_err, NULL},
 };
 
@@ -1565,6 +1571,12 @@ set_qf_format:
 			else
 				set_opt(sbi->s_mount_opt,NO_AUTO_DA_ALLOC);
 			break;
+		case Opt_discard:
+			set_opt(sbi->s_mount_opt, DISCARD);
+			break;
+		case Opt_nodiscard:
+			clear_opt(sbi->s_mount_opt, DISCARD);
+			break;
 		default:
 			ext4_msg(sb, KERN_ERR,
 			       "Unrecognized mount option \"%s\" "

[PATCH 1/2 V3] ext4: make trim/discard optional (and off by default)

[Eric Sandeen]

It is anticipated that when sb_issue_discard starts doing
real work on trim-capable devices, we may see issues.  Make
this mount-time optional, and default it to off until we know
that things are working out OK.

V2: rename "trim" to "discard" to match btrfs & gfs2
V3: fix mailer flowed text mangling, sorry.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 6d94e06..26904ff 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -353,6 +353,12 @@ noauto_da_alloc		replacing existing files via patterns such as
 			system crashes before the delayed allocation
 			blocks are forced to disk.
 
+discard		Controls whether ext4 should issue discard/TRIM
+nodiscard(*)		commands to the underlying block device when
+			blocks are freed.  This is useful for SSD devices
+			and sparse/thinly-provisioned LUNs, but it is off
+			by default until sufficient testing has been done.
+
 Data Mode
 =========
 There are 3 different data modes:
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 8825515..05ce38b 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -750,6 +750,7 @@ struct ext4_inode_info {
 #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 */
+#define EXT4_MOUNT_DISCARD		0x40000000 /* Issue DISCARD requests */
 
 #define clear_opt(o, opt)		o &= ~EXT4_MOUNT_##opt
 #define set_opt(o, opt)			o |= EXT4_MOUNT_##opt
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index bba1282..6e5a23a 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2529,7 +2529,6 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
 	struct ext4_group_info *db;
 	int err, count = 0, count2 = 0;
 	struct ext4_free_data *entry;
-	ext4_fsblk_t discard_block;
 	struct list_head *l, *ltmp;
 
 	list_for_each_safe(l, ltmp, &txn->t_private_list) {
@@ -2559,13 +2558,19 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
 			page_cache_release(e4b.bd_bitmap_page);
 		}
 		ext4_unlock_group(sb, entry->group);
-		discard_block = (ext4_fsblk_t) entry->group * EXT4_BLOCKS_PER_GROUP(sb)
-			+ entry->start_blk
-			+ le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
-		trace_ext4_discard_blocks(sb, (unsigned long long)discard_block,
-					  entry->count);
-		sb_issue_discard(sb, discard_block, entry->count);
-
+		if (test_opt(sb, DISCARD)) {
+			ext4_fsblk_t discard_block;
+			struct ext4_super_block *es = EXT4_SB(sb)->s_es;
+
+			discard_block = (ext4_fsblk_t)entry->group *
+						EXT4_BLOCKS_PER_GROUP(sb)
+					+ entry->start_blk
+					+ le32_to_cpu(es->s_first_data_block);
+			trace_ext4_discard_blocks(sb,
+					(unsigned long long)discard_block,
+					entry->count);
+			sb_issue_discard(sb, discard_block, entry->count);
+		}
 		kmem_cache_free(ext4_free_ext_cachep, entry);
 		ext4_mb_release_desc(&e4b);
 	}
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d4ca92a..b9638d9 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -899,6 +899,9 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
 	if (test_opt(sb, NO_AUTO_DA_ALLOC))
 		seq_puts(seq, ",noauto_da_alloc");
 
+	if (test_opt(sb, DISCARD))
+		seq_puts(seq, ",discard");
+
 	ext4_show_quota_options(seq, sb);
 
 	return 0;
@@ -1079,7 +1082,8 @@ enum {
 	Opt_usrquota, Opt_grpquota, Opt_i_version,
 	Opt_stripe, Opt_delalloc, Opt_nodelalloc,
 	Opt_block_validity, Opt_noblock_validity,
-	Opt_inode_readahead_blks, Opt_journal_ioprio
+	Opt_inode_readahead_blks, Opt_journal_ioprio,
+	Opt_discard, Opt_nodiscard,
 };
 
 static const match_table_t tokens = {
@@ -1144,6 +1148,8 @@ static const match_table_t tokens = {
 	{Opt_auto_da_alloc, "auto_da_alloc=%u"},
 	{Opt_auto_da_alloc, "auto_da_alloc"},
 	{Opt_noauto_da_alloc, "noauto_da_alloc"},
+	{Opt_discard, "discard"},
+	{Opt_nodiscard, "nodiscard"},
 	{Opt_err, NULL},
 };
 
@@ -1565,6 +1571,12 @@ set_qf_format:
 			else
 				set_opt(sbi->s_mount_opt,NO_AUTO_DA_ALLOC);
 			break;
+		case Opt_discard:
+			set_opt(sbi->s_mount_opt, DISCARD);
+			break;
+		case Opt_nodiscard:
+			clear_opt(sbi->s_mount_opt, DISCARD);
+			break;
 		default:
 			ext4_msg(sb, KERN_ERR,
 			       "Unrecognized mount option \"%s\" "

Re: [PATCH 1/2 V3] ext4: make trim/discard optional (and off by default)

[tytso]

On Tue, Nov 17, 2009 at 11:05:01AM -0600, Eric Sandeen wrote:
> It is anticipated that when sb_issue_discard starts doing
> real work on trim-capable devices, we may see issues.  Make
> this mount-time optional, and default it to off until we know
> that things are working out OK.
> 
> V2: rename "trim" to "discard" to match btrfs & gfs2
> V3: fix mailer flowed text mangling, sorry.
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>

Queued, thanks.

						- Ted