[PATCH] ext4: introduce EXT4_BG_WAS_TRIMMED to optimize trim

[Wang Shilong <wangshilong1991@gmail.com>]

From: Wang Shilong <wshilong@ddn.com>

Currently WAS_TRIMMED flag is not persistent, whenever filesystem was
remounted, fstrim need walk all block groups again, the problem with
this is FSTRIM could be slow on very large LUN SSD based filesystem.

To avoid this kind of problem, we introduce a block group flag
EXT4_BG_WAS_TRIMMED, the side effect of this is we need introduce
extra one block group dirty write after trimming block group.

And When clearing TRIMMED flag, block group will be journalled
anyway, so it won't introduce any overhead.

Cc: Shuichi Ihara <sihara@ddn.com>
Cc: Andreas Dilger <adilger@dilger.ca>
Cc: Wang Shilong <wangshilong1991@gmail.com>
Signed-off-by: Wang Shilong <wshilong@ddn.com>
---
 fs/ext4/ext4.h      | 18 +++++++--------
 fs/ext4/ext4_jbd2.h |  3 ++-
 fs/ext4/mballoc.c   | 54 ++++++++++++++++++++++++++++++++++-----------
 3 files changed, 52 insertions(+), 23 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index ad2dbf6e4924..23c2dc529a28 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -357,6 +357,7 @@ struct flex_groups {
 #define EXT4_BG_INODE_UNINIT	0x0001 /* Inode table/bitmap not in use */
 #define EXT4_BG_BLOCK_UNINIT	0x0002 /* Block bitmap not in use */
 #define EXT4_BG_INODE_ZEROED	0x0004 /* On-disk itable initialized to zero */
+#define EXT4_BG_WAS_TRIMMED	0x0008 /* block group was trimmed */
 
 /*
  * Macro-instructions used to manage group descriptors
@@ -3112,9 +3113,8 @@ struct ext4_group_info {
 };
 
 #define EXT4_GROUP_INFO_NEED_INIT_BIT		0
-#define EXT4_GROUP_INFO_WAS_TRIMMED_BIT		1
-#define EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT	2
-#define EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT	3
+#define EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT	1
+#define EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT	2
 #define EXT4_GROUP_INFO_BBITMAP_CORRUPT		\
 	(1 << EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT)
 #define EXT4_GROUP_INFO_IBITMAP_CORRUPT		\
@@ -3127,12 +3127,12 @@ struct ext4_group_info {
 #define EXT4_MB_GRP_IBITMAP_CORRUPT(grp)	\
 	(test_bit(EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT, &((grp)->bb_state)))
 
-#define EXT4_MB_GRP_WAS_TRIMMED(grp)	\
-	(test_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state)))
-#define EXT4_MB_GRP_SET_TRIMMED(grp)	\
-	(set_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state)))
-#define EXT4_MB_GRP_CLEAR_TRIMMED(grp)	\
-	(clear_bit(EXT4_GROUP_INFO_WAS_TRIMMED_BIT, &((grp)->bb_state)))
+#define EXT4_MB_GDP_WAS_TRIMMED(gdp)	\
+	(gdp->bg_flags & cpu_to_le16(EXT4_BG_WAS_TRIMMED))
+#define EXT4_MB_GDP_SET_TRIMMED(gdp)	\
+	(gdp->bg_flags |= cpu_to_le16(EXT4_BG_WAS_TRIMMED))
+#define EXT4_MB_GDP_CLEAR_TRIMMED(gdp)	\
+	(gdp->bg_flags &= ~cpu_to_le16(EXT4_BG_WAS_TRIMMED))
 
 #define EXT4_MAX_CONTENTION		8
 #define EXT4_CONTENTION_THRESHOLD	2
diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
index 4b9002f0e84c..4094a5b247f7 100644
--- a/fs/ext4/ext4_jbd2.h
+++ b/fs/ext4/ext4_jbd2.h
@@ -123,7 +123,8 @@
 #define EXT4_HT_MOVE_EXTENTS     9
 #define EXT4_HT_XATTR           10
 #define EXT4_HT_EXT_CONVERT     11
-#define EXT4_HT_MAX             12
+#define EXT4_HT_FS_TRIM		12
+#define EXT4_HT_MAX             13
 
 /**
  *   struct ext4_journal_cb_entry - Base structure for callback information.
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 30d5d97548c4..d25377948994 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2829,15 +2829,6 @@ static void ext4_free_data_in_buddy(struct super_block *sb,
 	rb_erase(&entry->efd_node, &(db->bb_free_root));
 	mb_free_blocks(NULL, &e4b, entry->efd_start_cluster, entry->efd_count);
 
-	/*
-	 * Clear the trimmed flag for the group so that the next
-	 * ext4_trim_fs can trim it.
-	 * If the volume is mounted with -o discard, online discard
-	 * is supported and the free blocks will be trimmed online.
-	 */
-	if (!test_opt(sb, DISCARD))
-		EXT4_MB_GRP_CLEAR_TRIMMED(db);
-
 	if (!db->bb_free_root.rb_node) {
 		/* No more items in the per group rb tree
 		 * balance refcounts from ext4_mb_free_metadata()
@@ -4928,8 +4919,7 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
 					 " group:%d block:%d count:%lu failed"
 					 " with %d", block_group, bit, count,
 					 err);
-		} else
-			EXT4_MB_GRP_CLEAR_TRIMMED(e4b.bd_info);
+		}
 
 		ext4_lock_group(sb, block_group);
 		mb_clear_bits(bitmap_bh->b_data, bit, count_clusters);
@@ -4939,6 +4929,14 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
 	ret = ext4_free_group_clusters(sb, gdp) + count_clusters;
 	ext4_free_group_clusters_set(sb, gdp, ret);
 	ext4_block_bitmap_csum_set(sb, block_group, gdp, bitmap_bh);
+	/*
+	 * Clear the trimmed flag for the group so that the next
+	 * ext4_trim_fs can trim it.
+	 * If the volume is mounted with -o discard, online discard
+	 * is supported and the free blocks will be trimmed online.
+	 */
+	if (!test_opt(sb, DISCARD))
+		EXT4_MB_GDP_CLEAR_TRIMMED(gdp);
 	ext4_group_desc_csum_set(sb, block_group, gdp);
 	ext4_unlock_group(sb, block_group);
 
@@ -5192,8 +5190,15 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
 	ext4_grpblk_t next, count = 0, free_count = 0;
 	struct ext4_buddy e4b;
 	int ret = 0;
+	struct ext4_group_desc *gdp;
+	struct buffer_head *gdp_bh;
 
 	trace_ext4_trim_all_free(sb, group, start, max);
+	gdp = ext4_get_group_desc(sb, group, &gdp_bh);
+	if (!gdp) {
+		ret = -EIO;
+		return ret;
+	}
 
 	ret = ext4_mb_load_buddy(sb, group, &e4b);
 	if (ret) {
@@ -5204,7 +5209,7 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
 	bitmap = e4b.bd_bitmap;
 
 	ext4_lock_group(sb, group);
-	if (EXT4_MB_GRP_WAS_TRIMMED(e4b.bd_info) &&
+	if (EXT4_MB_GDP_WAS_TRIMMED(gdp) &&
 	    minblocks >= atomic_read(&EXT4_SB(sb)->s_last_trim_minblks))
 		goto out;
 
@@ -5245,12 +5250,35 @@ ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
 
 	if (!ret) {
 		ret = count;
-		EXT4_MB_GRP_SET_TRIMMED(e4b.bd_info);
+		EXT4_MB_GDP_SET_TRIMMED(gdp);
+		ext4_group_desc_csum_set(sb, group, gdp);
 	}
 out:
 	ext4_unlock_group(sb, group);
 	ext4_mb_unload_buddy(&e4b);
+	if (ret > 0) {
+		int err;
+		handle_t *handle;
 
+		handle = ext4_journal_start_sb(sb, EXT4_HT_FS_TRIM, 1);
+		if (IS_ERR(handle)) {
+			ret = PTR_ERR(handle);
+			goto out_return;
+		}
+		err = ext4_journal_get_write_access(handle, gdp_bh);
+		if (err) {
+			ret = err;
+			goto out_journal;
+		}
+		err = ext4_handle_dirty_metadata(handle, NULL, gdp_bh);
+		if (err)
+			ret = err;
+out_journal:
+		err = ext4_journal_stop(handle);
+		if (err)
+			ret = err;
+	}
+out_return:
 	ext4_debug("trimmed %d blocks in the group %d\n",
 		count, group);
 
-- 
2.25.4