[PATCH RFC] f2fs: combine nat_bits and free_nid_bitmap cache

[Chao Yu]

Both nat_bits cache and free_nid_bitmap cache provide same functionality
as a intermediate cache between free nid cache and disk, but with
different granularity of indicating free nid range, and different
persistence policy. nat_bits cache provides better persistence ability,
and free_nid_bitmap provides better granularity.

In this patch we combine advantage of both caches, so finally policy of
the intermediate cache would be:
- init: load free nid status from nat_bits into free_nid_bitmap
- lookup: scan free_nid_bitmap before load NAT blocks
- update: update free_nid_bitmap in real-time
- persistence: udpate and persist nat_bits in checkpoint

Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
---
 fs/f2fs/node.c | 109 +++++++++++++++++++++------------------------------------
 1 file changed, 39 insertions(+), 70 deletions(-)

diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 1a759d45b7e4..6c027b6833f4 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -338,9 +338,6 @@ static void set_node_addr(struct f2fs_sb_info *sbi, struct node_info *ni,
 		set_nat_flag(e, IS_CHECKPOINTED, false);
 	__set_nat_cache_dirty(nm_i, e);
 
-	if (enabled_nat_bits(sbi, NULL) && new_blkaddr == NEW_ADDR)
-		clear_bit_le(NAT_BLOCK_OFFSET(ni->nid), nm_i->empty_nat_bits);
-
 	/* update fsync_mark if its inode nat entry is still alive */
 	if (ni->nid != ni->ino)
 		e = __lookup_nat_cache(nm_i, ni->ino);
@@ -1920,58 +1917,6 @@ static void scan_free_nid_bits(struct f2fs_sb_info *sbi)
 	up_read(&nm_i->nat_tree_lock);
 }
 
-static int scan_nat_bits(struct f2fs_sb_info *sbi)
-{
-	struct f2fs_nm_info *nm_i = NM_I(sbi);
-	struct page *page;
-	unsigned int i = 0;
-	nid_t nid;
-
-	if (!enabled_nat_bits(sbi, NULL))
-		return -EAGAIN;
-
-	down_read(&nm_i->nat_tree_lock);
-check_empty:
-	i = find_next_bit_le(nm_i->empty_nat_bits, nm_i->nat_blocks, i);
-	if (i >= nm_i->nat_blocks) {
-		i = 0;
-		goto check_partial;
-	}
-
-	for (nid = i * NAT_ENTRY_PER_BLOCK; nid < (i + 1) * NAT_ENTRY_PER_BLOCK;
-									nid++) {
-		if (unlikely(nid >= nm_i->max_nid))
-			break;
-		add_free_nid(sbi, nid, true);
-	}
-
-	if (nm_i->nid_cnt[FREE_NID_LIST] >= MAX_FREE_NIDS)
-		goto out;
-	i++;
-	goto check_empty;
-
-check_partial:
-	i = find_next_zero_bit_le(nm_i->full_nat_bits, nm_i->nat_blocks, i);
-	if (i >= nm_i->nat_blocks) {
-		disable_nat_bits(sbi, true);
-		up_read(&nm_i->nat_tree_lock);
-		return -EINVAL;
-	}
-
-	nid = i * NAT_ENTRY_PER_BLOCK;
-	page = get_current_nat_page(sbi, nid);
-	scan_nat_page(sbi, page, nid);
-	f2fs_put_page(page, 1);
-
-	if (nm_i->nid_cnt[FREE_NID_LIST] < MAX_FREE_NIDS) {
-		i++;
-		goto check_partial;
-	}
-out:
-	up_read(&nm_i->nat_tree_lock);
-	return 0;
-}
-
 static void __build_free_nids(struct f2fs_sb_info *sbi, bool sync, bool mount)
 {
 	struct f2fs_nm_info *nm_i = NM_I(sbi);
@@ -1993,21 +1938,6 @@ static void __build_free_nids(struct f2fs_sb_info *sbi, bool sync, bool mount)
 
 		if (nm_i->nid_cnt[FREE_NID_LIST])
 			return;
-
-		/* try to find free nids with nat_bits */
-		if (!scan_nat_bits(sbi) && nm_i->nid_cnt[FREE_NID_LIST])
-			return;
-	}
-
-	/* find next valid candidate */
-	if (enabled_nat_bits(sbi, NULL)) {
-		int idx = find_next_zero_bit_le(nm_i->full_nat_bits,
-					nm_i->nat_blocks, 0);
-
-		if (idx >= nm_i->nat_blocks)
-			set_sbi_flag(sbi, SBI_NEED_FSCK);
-		else
-			nid = idx * NAT_ENTRY_PER_BLOCK;
 	}
 
 	/* readahead nat pages to be scanned */
@@ -2590,6 +2520,41 @@ static int __get_nat_bitmaps(struct f2fs_sb_info *sbi)
 	return 0;
 }
 
+inline void load_free_nid_bitmap(struct f2fs_sb_info *sbi)
+{
+	struct f2fs_nm_info *nm_i = NM_I(sbi);
+	unsigned int i = 0;
+	nid_t nid, last_nid;
+
+	for (i = 0; i < nm_i->nat_blocks; i++) {
+		i = find_next_bit_le(nm_i->empty_nat_bits, nm_i->nat_blocks, i);
+		if (i >= nm_i->nat_blocks)
+			break;
+
+		set_bit_le(i, nm_i->nat_block_bitmap);
+
+		nid = i * NAT_ENTRY_PER_BLOCK;
+		last_nid = (i + 1) * NAT_ENTRY_PER_BLOCK;
+
+		for (; nid < last_nid; nid++)
+			update_free_nid_bitmap(sbi, nid, true, true);
+	}
+
+	for (i = 0; i < nm_i->nat_blocks; i++) {
+		i = find_next_bit_le(nm_i->full_nat_bits, nm_i->nat_blocks, i);
+		if (i >= nm_i->nat_blocks)
+			break;
+
+		set_bit_le(i, nm_i->nat_block_bitmap);
+
+		nid = i * NAT_ENTRY_PER_BLOCK;
+		last_nid = (i + 1) * NAT_ENTRY_PER_BLOCK;
+
+		for (; nid < last_nid; nid++)
+			update_free_nid_bitmap(sbi, nid, false, true);
+	}
+}
+
 static int init_node_manager(struct f2fs_sb_info *sbi)
 {
 	struct f2fs_super_block *sb_raw = F2FS_RAW_SUPER(sbi);
@@ -2672,6 +2637,10 @@ int init_free_nid_cache(struct f2fs_sb_info *sbi)
 
 	spin_lock_init(&nm_i->free_nid_lock);
 
+	/* load free nid status from nat_bits table */
+	if (enabled_nat_bits(sbi, NULL))
+		load_free_nid_bitmap(sbi);
+
 	return 0;
 }
 
-- 
2.8.2.295.g3f1c1d0