f2fs: introduce sysfs atomic write statistics

introduce the below 4 new sysfs node for atomic write statistics.
- current_atomic_write: the total current atomic write block count,
                        which is not committed yet.
- peak_atomic_write: the peak value of total current atomic write block
                     count after boot.
- committed_atomic_block: the accumulated total committed atomic write
                          block count after boot.
- revoked_atomic_block: the accumulated total revoked atomic write block
                        count after boot.
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Documentation/ABI/testing/sysfs-fs-f2fs

@@ -586,3 +586,27 @@ Date:		June 2022
 Contact:	"Jaegeuk Kim" <jaegeuk@kernel.org>
 Description:	Shows the number of unusable blocks in a section which was defined by
 		the zone capacity reported by underlying zoned device.
+
+What:		/sys/fs/f2fs/<disk>/current_atomic_write
+Date:		July 2022
+Contact:	"Daeho Jeong" <daehojeong@google.com>
+Description:	Show the total current atomic write block count, which is not committed yet.
+		This is a read-only entry.
+
+What:		/sys/fs/f2fs/<disk>/peak_atomic_write
+Date:		July 2022
+Contact:	"Daeho Jeong" <daehojeong@google.com>
+Description:	Show the peak value of total current atomic write block count after boot.
+		If you write "0" here, you can initialize to "0".
+
+What:		/sys/fs/f2fs/<disk>/committed_atomic_block
+Date:		July 2022
+Contact:	"Daeho Jeong" <daehojeong@google.com>
+Description:	Show the accumulated total committed atomic write block count after boot.
+		If you write "0" here, you can initialize to "0".
+
+What:		/sys/fs/f2fs/<disk>/revoked_atomic_block
+Date:		July 2022
+Contact:	"Daeho Jeong" <daehojeong@google.com>
+Description:	Show the accumulated total revoked atomic write block count after boot.
+		If you write "0" here, you can initialize to "0".

fs/f2fs/data.c

@@ -3406,12 +3406,11 @@ static int prepare_atomic_write_begin(struct f2fs_sb_info *sbi,
 	struct inode *cow_inode = F2FS_I(inode)->cow_inode;
 	pgoff_t index = page->index;
 	int err = 0;
-	block_t ori_blk_addr;
+	block_t ori_blk_addr = NULL_ADDR;
 
 	/* If pos is beyond the end of file, reserve a new block in COW inode */
 	if ((pos & PAGE_MASK) >= i_size_read(inode))
-		return __reserve_data_block(cow_inode, index, blk_addr,
-					node_changed);
+		goto reserve_block;
 
 	/* Look for the block in COW inode first */
 	err = __find_data_block(cow_inode, index, blk_addr);
@@ -3425,10 +3424,12 @@ static int prepare_atomic_write_begin(struct f2fs_sb_info *sbi,
 	if (err)
 		return err;
 
+reserve_block:
 	/* Finally, we should reserve a new block in COW inode for the update */
 	err = __reserve_data_block(cow_inode, index, blk_addr, node_changed);
 	if (err)
 		return err;
+	inc_atomic_write_cnt(inode);
 
 	if (ori_blk_addr != NULL_ADDR)
 		*blk_addr = ori_blk_addr;

fs/f2fs/f2fs.h

@@ -813,6 +813,8 @@ struct f2fs_inode_info {
 	unsigned char i_compress_level;		/* compress level (lz4hc,zstd) */
 	unsigned short i_compress_flag;		/* compress flag */
 	unsigned int i_cluster_size;		/* cluster size */
+
+	unsigned int atomic_write_cnt;
 };
 
 static inline void get_extent_info(struct extent_info *ext,
@@ -1813,6 +1815,12 @@ struct f2fs_sb_info {
 	int max_fragment_chunk;			/* max chunk size for block fragmentation mode */
 	int max_fragment_hole;			/* max hole size for block fragmentation mode */
 
+	/* For atomic write statistics */
+	atomic64_t current_atomic_write;
+	s64 peak_atomic_write;
+	u64 committed_atomic_block;
+	u64 revoked_atomic_block;
+
 #ifdef CONFIG_F2FS_FS_COMPRESSION
 	struct kmem_cache *page_array_slab;	/* page array entry */
 	unsigned int page_array_slab_size;	/* default page array slab size */
@@ -2427,6 +2435,28 @@ static inline void inode_dec_dirty_pages(struct inode *inode)
 		dec_page_count(F2FS_I_SB(inode), F2FS_DIRTY_QDATA);
 }
 
+static inline void inc_atomic_write_cnt(struct inode *inode)
+{
+	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
+	struct f2fs_inode_info *fi = F2FS_I(inode);
+	u64 current_write;
+
+	fi->atomic_write_cnt++;
+	atomic64_inc(&sbi->current_atomic_write);
+	current_write = atomic64_read(&sbi->current_atomic_write);
+	if (current_write > sbi->peak_atomic_write)
+		sbi->peak_atomic_write = current_write;
+}
+
+static inline void release_atomic_write_cnt(struct inode *inode)
+{
+	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
+	struct f2fs_inode_info *fi = F2FS_I(inode);
+
+	atomic64_sub(fi->atomic_write_cnt, &sbi->current_atomic_write);
+	fi->atomic_write_cnt = 0;
+}
+
 static inline s64 get_pages(struct f2fs_sb_info *sbi, int count_type)
 {
 	return atomic_read(&sbi->nr_pages[count_type]);

fs/f2fs/file.c

@@ -2075,6 +2075,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
 	f2fs_update_time(sbi, REQ_TIME);
 	fi->atomic_write_task = current;
 	stat_update_max_atomic_write(inode);
+	fi->atomic_write_cnt = 0;
 out:
 	inode_unlock(inode);
 	mnt_drop_write_file(filp);

fs/f2fs/segment.c

@@ -196,6 +196,7 @@ void f2fs_abort_atomic_write(struct inode *inode, bool clean)
 		clear_inode_flag(fi->cow_inode, FI_ATOMIC_FILE);
 		iput(fi->cow_inode);
 		fi->cow_inode = NULL;
+		release_atomic_write_cnt(inode);
 		clear_inode_flag(inode, FI_ATOMIC_FILE);
 
 		spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
@@ -335,6 +336,11 @@ static int __f2fs_commit_atomic_write(struct inode *inode)
 	}
 
 out:
+	if (ret)
+		sbi->revoked_atomic_block += fi->atomic_write_cnt;
+	else
+		sbi->committed_atomic_block += fi->atomic_write_cnt;
+
 	__complete_revoke_list(inode, &revoke_list, ret ? true : false);
 
 	return ret;

fs/f2fs/super.c

@@ -3615,6 +3615,7 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
 	sbi->max_fragment_chunk = DEF_FRAGMENT_SIZE;
 	sbi->max_fragment_hole = DEF_FRAGMENT_SIZE;
 	spin_lock_init(&sbi->gc_urgent_high_lock);
+	atomic64_set(&sbi->current_atomic_write, 0);
 
 	sbi->dir_level = DEF_DIR_LEVEL;
 	sbi->interval_time[CP_TIME] = DEF_CP_INTERVAL;

fs/f2fs/sysfs.c

@@ -339,6 +339,21 @@ static ssize_t f2fs_sbi_show(struct f2fs_attr *a,
 			sbi->gc_reclaimed_segs[sbi->gc_segment_mode]);
 	}
 
+	if (!strcmp(a->attr.name, "current_atomic_write")) {
+		s64 current_write = atomic64_read(&sbi->current_atomic_write);
+
+		return sysfs_emit(buf, "%lld\n", current_write);
+	}
+
+	if (!strcmp(a->attr.name, "peak_atomic_write"))
+		return sysfs_emit(buf, "%lld\n", sbi->peak_atomic_write);
+
+	if (!strcmp(a->attr.name, "committed_atomic_block"))
+		return sysfs_emit(buf, "%llu\n", sbi->committed_atomic_block);
+
+	if (!strcmp(a->attr.name, "revoked_atomic_block"))
+		return sysfs_emit(buf, "%llu\n", sbi->revoked_atomic_block);
+
 	ui = (unsigned int *)(ptr + a->offset);
 
 	return sprintf(buf, "%u\n", *ui);
@@ -608,6 +623,27 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
 		return count;
 	}
 
+	if (!strcmp(a->attr.name, "peak_atomic_write")) {
+		if (t != 0)
+			return -EINVAL;
+		sbi->peak_atomic_write = 0;
+		return count;
+	}
+
+	if (!strcmp(a->attr.name, "committed_atomic_block")) {
+		if (t != 0)
+			return -EINVAL;
+		sbi->committed_atomic_block = 0;
+		return count;
+	}
+
+	if (!strcmp(a->attr.name, "revoked_atomic_block")) {
+		if (t != 0)
+			return -EINVAL;
+		sbi->revoked_atomic_block = 0;
+		return count;
+	}
+
 	*ui = (unsigned int)t;
 
 	return count;
@@ -855,6 +891,12 @@ F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, gc_reclaimed_segments, gc_reclaimed_segs);
 F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, max_fragment_chunk, max_fragment_chunk);
 F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, max_fragment_hole, max_fragment_hole);
 
+/* For atomic write */
+F2FS_RO_ATTR(F2FS_SBI, f2fs_sb_info, current_atomic_write, current_atomic_write);
+F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, peak_atomic_write, peak_atomic_write);
+F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, committed_atomic_block, committed_atomic_block);
+F2FS_RW_ATTR(F2FS_SBI, f2fs_sb_info, revoked_atomic_block, revoked_atomic_block);
+
 #define ATTR_LIST(name) (&f2fs_attr_##name.attr)
 static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(gc_urgent_sleep_time),
@@ -944,6 +986,10 @@ static struct attribute *f2fs_attrs[] = {
 	ATTR_LIST(gc_reclaimed_segments),
 	ATTR_LIST(max_fragment_chunk),
 	ATTR_LIST(max_fragment_hole),
+	ATTR_LIST(current_atomic_write),
+	ATTR_LIST(peak_atomic_write),
+	ATTR_LIST(committed_atomic_block),
+	ATTR_LIST(revoked_atomic_block),
 	NULL,
 };
 ATTRIBUTE_GROUPS(f2fs);