[RFC PATCH] exfat: optimize performance of deleting a file

[Jun <hljhnu@gmail.com>]

When a large file is deleted, it's cluster bitmap is cleared.
After a bit is cleared, the buffer_head is synced.
A buffer_head can be synced many times repeatedly.
We can clear all bits first and then sync all buffer_heads.
So each buffer_head is synced only once, which significantly improves performance.

In my test, It takes about 2 minitues to delete a 5GB file without the patch.
After applying the patch, the file is deleted in almost less than 1s.

Signed-off-by: Jun <hljhnu@gmail.com>
Change-Id: I7637032db04042b8ad1ca73fe7db09d43a253255
---
 fs/exfat/balloc.c   | 28 ++++++++++++++++++++++++++--
 fs/exfat/exfat_fs.h |  2 ++
 fs/exfat/fatent.c   | 45 +++++++++++++++++++++++++++++++++++++++++----
 3 files changed, 69 insertions(+), 6 deletions(-)

diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c
index 579c10f57c2b..58bdfb58bf1d 100644
--- a/fs/exfat/balloc.c
+++ b/fs/exfat/balloc.c
@@ -164,7 +164,6 @@ void exfat_clear_bitmap(struct inode *inode, unsigned int clu)
 	unsigned int ent_idx;
 	struct super_block *sb = inode->i_sb;
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
-	struct exfat_mount_options *opts = &sbi->options;
 
 	WARN_ON(clu < EXFAT_FIRST_CLUSTER);
 	ent_idx = CLUSTER_TO_BITMAP_ENT(clu);
@@ -172,7 +171,32 @@ void exfat_clear_bitmap(struct inode *inode, unsigned int clu)
 	b = BITMAP_OFFSET_BIT_IN_SECTOR(sb, ent_idx);
 
 	clear_bit_le(b, sbi->vol_amap[i]->b_data);
-	exfat_update_bh(sbi->vol_amap[i], IS_DIRSYNC(inode));
+	set_buffer_uptodate(sbi->vol_amap[i]);
+	mark_buffer_dirty(sbi->vol_amap[i]);
+}
+
+void exfat_wait_bitmap(struct inode *inode, unsigned int clu)
+{
+	int i;
+	unsigned int ent_idx;
+	struct super_block *sb = inode->i_sb;
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+
+	WARN_ON(clu < EXFAT_FIRST_CLUSTER);
+	ent_idx = CLUSTER_TO_BITMAP_ENT(clu);
+	i = BITMAP_OFFSET_SECTOR_INDEX(sb, ent_idx);
+
+	if (IS_DIRSYNC(inode))
+		sync_dirty_buffer(sbi->vol_amap[i]);
+}
+
+void exfat_discard_cluster(struct inode *inode, unsigned int clu)
+{
+	struct super_block *sb = inode->i_sb;
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+	struct exfat_mount_options *opts = &sbi->options;
+
+	WARN_ON(clu < EXFAT_FIRST_CLUSTER);
 
 	if (opts->discard) {
 		int ret_discard;
diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
index b8f0e829ecbd..1ecd2379022d 100644
--- a/fs/exfat/exfat_fs.h
+++ b/fs/exfat/exfat_fs.h
@@ -409,6 +409,8 @@ int exfat_load_bitmap(struct super_block *sb);
 void exfat_free_bitmap(struct exfat_sb_info *sbi);
 int exfat_set_bitmap(struct inode *inode, unsigned int clu);
 void exfat_clear_bitmap(struct inode *inode, unsigned int clu);
+void exfat_wait_bitmap(struct inode *inode, unsigned int clu);
+void exfat_discard_cluster(struct inode *inode, unsigned int clu);
 unsigned int exfat_find_free_bitmap(struct super_block *sb, unsigned int clu);
 int exfat_count_used_clusters(struct super_block *sb, unsigned int *ret_count);
 
diff --git a/fs/exfat/fatent.c b/fs/exfat/fatent.c
index c3c9afee7418..f39a912a7da7 100644
--- a/fs/exfat/fatent.c
+++ b/fs/exfat/fatent.c
@@ -183,19 +183,56 @@ int exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain)
 
 			num_clusters++;
 		} while (num_clusters < p_chain->size);
+		sbi->used_clusters -= num_clusters;
+
+		clu = p_chain->dir;
+		num_clusters = 0;
+		do {
+			exfat_wait_bitmap(inode, clu);
+			clu++;
+
+			num_clusters++;
+		} while (num_clusters < p_chain->size);
+
+		clu = p_chain->dir;
+		num_clusters = 0;
+		do {
+			exfat_discard_cluster(inode, clu);
+			clu++;
+
+			num_clusters++;
+		} while (num_clusters < p_chain->size);
+
 	} else {
 		do {
 			exfat_clear_bitmap(inode, clu);
 
 			if (exfat_get_next_cluster(sb, &clu))
-				goto dec_used_clus;
+				goto exit;
+
+			sbi->used_clusters--;
+		} while (clu != EXFAT_EOF_CLUSTER);
+
+		clu = p_chain->dir;
+		do {
+			exfat_wait_bitmap(inode, clu);
+
+			if (exfat_get_next_cluster(sb, &clu))
+				goto exit;
+
+		} while (clu != EXFAT_EOF_CLUSTER);
+
+		clu = p_chain->dir;
+		do {
+			exfat_discard_cluster(inode, clu);
+
+			if (exfat_get_next_cluster(sb, &clu))
+				goto exit;
 
-			num_clusters++;
 		} while (clu != EXFAT_EOF_CLUSTER);
 	}
 
-dec_used_clus:
-	sbi->used_clusters -= num_clusters;
+exit:
 	return 0;
 }
 
-- 
2.36.1