[PATCH v2] f2fs: don't wait writeback for datas during checkpoint

[Chao Yu]

Normally, while committing checkpoint, we will wait on all pages to be
writebacked no matter the page is data or metadata, so in scenario where
there are lots of data IO being submitted with metadata, we may suffer
long latency for waiting writeback during checkpoint.

Indeed, we only care about persistence for pages with metadata, but not
pages with data, as file system consistent are only related to metadate,
so in order to avoid encountering long latency in above scenario, let's
recognize and reference metadata in submitted IOs, wait writeback only
for metadatas.

Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
---
 fs/f2fs/checkpoint.c |  2 +-
 fs/f2fs/data.c       | 36 ++++++++++++++++++++++++++++++++----
 fs/f2fs/debug.c      |  7 ++++---
 fs/f2fs/f2fs.h       |  8 +++++---
 4 files changed, 42 insertions(+), 11 deletions(-)

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 7bece59..bdf8a50 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1003,7 +1003,7 @@ static void wait_on_all_pages_writeback(struct f2fs_sb_info *sbi)
 	for (;;) {
 		prepare_to_wait(&sbi->cp_wait, &wait, TASK_UNINTERRUPTIBLE);
 
-		if (!atomic_read(&sbi->nr_wb_bios))
+		if (!get_pages(sbi, F2FS_WB_META))
 			break;
 
 		io_schedule_timeout(5*HZ);
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 66d2aee..f52cec3 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -29,6 +29,26 @@
 #include "trace.h"
 #include <trace/events/f2fs.h>
 
+static bool f2fs_is_meta_data(struct page *page)
+{
+	struct address_space *mapping = page->mapping;
+	struct f2fs_sb_info *sbi;
+	struct inode *inode;
+
+	/* it is bounce page of encrypted regular inode */
+	if (!mapping)
+		return false;
+
+	inode = mapping->host;
+	sbi = F2FS_I_SB(inode);
+
+	if ((inode->i_ino == F2FS_META_INO(sbi) &&
+			page->index < MAIN_BLKADDR(sbi)) ||
+			inode->i_ino ==  F2FS_NODE_INO(sbi) ||
+			S_ISDIR(inode->i_mode))
+		return true;
+	return false;
+}
 static void f2fs_read_end_io(struct bio *bio)
 {
 	struct bio_vec *bvec;
@@ -73,6 +93,7 @@ static void f2fs_write_end_io(struct bio *bio)
 
 	bio_for_each_segment_all(bvec, bio, i) {
 		struct page *page = bvec->bv_page;
+		bool is_meta = f2fs_is_meta_data(page);
 
 		fscrypt_pullback_bio_page(&page, true);
 
@@ -80,9 +101,10 @@ static void f2fs_write_end_io(struct bio *bio)
 			mapping_set_error(page->mapping, -EIO);
 			f2fs_stop_checkpoint(sbi, true);
 		}
+		dec_page_count(sbi, is_meta ? F2FS_WB_META : F2FS_WB_DATA);
 		end_page_writeback(page);
 	}
-	if (atomic_dec_and_test(&sbi->nr_wb_bios) &&
+	if (!get_pages(sbi, F2FS_WB_META) &&
 				wq_has_sleeper(&sbi->cp_wait))
 		wake_up(&sbi->cp_wait);
 
@@ -111,7 +133,6 @@ static inline void __submit_bio(struct f2fs_sb_info *sbi,
 				struct bio *bio, enum page_type type)
 {
 	if (!is_read_io(bio_op(bio))) {
-		atomic_inc(&sbi->nr_wb_bios);
 		if (f2fs_sb_mounted_blkzoned(sbi->sb) &&
 			current->plug && (type == DATA || type == NODE))
 			blk_finish_plug(current->plug);
@@ -272,6 +293,15 @@ void f2fs_submit_page_mbio(struct f2fs_io_info *fio)
 		verify_block_addr(sbi, fio->old_blkaddr);
 	verify_block_addr(sbi, fio->new_blkaddr);
 
+	bio_page = fio->encrypted_page ? fio->encrypted_page : fio->page;
+
+	if (!is_read) {
+		bool is_meta;
+
+		is_meta = f2fs_is_meta_data(bio_page);
+		inc_page_count(sbi, is_meta ? F2FS_WB_META : F2FS_WB_DATA);
+	}
+
 	down_write(&io->io_rwsem);
 
 	if (io->bio && (io->last_block_in_bio != fio->new_blkaddr - 1 ||
@@ -284,8 +314,6 @@ void f2fs_submit_page_mbio(struct f2fs_io_info *fio)
 		io->fio = *fio;
 	}
 
-	bio_page = fio->encrypted_page ? fio->encrypted_page : fio->page;
-
 	if (bio_add_page(io->bio, bio_page, PAGE_SIZE, 0) <
 							PAGE_SIZE) {
 		__submit_merged_bio(io);
diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
index 2fdf233..f2d87de 100644
--- a/fs/f2fs/debug.c
+++ b/fs/f2fs/debug.c
@@ -50,7 +50,8 @@ static void update_general_status(struct f2fs_sb_info *sbi)
 	si->ndirty_files = sbi->ndirty_inode[FILE_INODE];
 	si->ndirty_all = sbi->ndirty_inode[DIRTY_META];
 	si->inmem_pages = get_pages(sbi, F2FS_INMEM_PAGES);
-	si->wb_bios = atomic_read(&sbi->nr_wb_bios);
+	si->nr_wb_meta = get_pages(sbi, F2FS_WB_META);
+	si->nr_wb_data = get_pages(sbi, F2FS_WB_DATA);
 	si->total_count = (int)sbi->user_block_count / sbi->blocks_per_seg;
 	si->rsvd_segs = reserved_segments(sbi);
 	si->overp_segs = overprovision_segments(sbi);
@@ -313,8 +314,8 @@ static int stat_show(struct seq_file *s, void *v)
 		seq_printf(s, "  - Inner Struct Count: tree: %d(%d), node: %d\n",
 				si->ext_tree, si->zombie_tree, si->ext_node);
 		seq_puts(s, "\nBalancing F2FS Async:\n");
-		seq_printf(s, "  - inmem: %4d, wb_bios: %4d\n",
-			   si->inmem_pages, si->wb_bios);
+		seq_printf(s, "  - inmem: %4d, wb_meta: %4d, wb_data: %4d\n",
+			   si->inmem_pages, si->nr_wb_meta, si->nr_wb_data);
 		seq_printf(s, "  - nodes: %4d in %4d\n",
 			   si->ndirty_node, si->node_pages);
 		seq_printf(s, "  - dents: %4d in dirs:%4d (%4d)\n",
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 23a937f..4df301c 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -682,6 +682,8 @@ enum count_type {
 	F2FS_DIRTY_META,
 	F2FS_INMEM_PAGES,
 	F2FS_DIRTY_IMETA,
+	F2FS_WB_META,
+	F2FS_WB_DATA,
 	NR_COUNT_TYPE,
 };
 
@@ -849,7 +851,6 @@ struct f2fs_sb_info {
 	block_t discard_blks;			/* discard command candidats */
 	block_t last_valid_block_count;		/* for recovery */
 	u32 s_next_generation;			/* for NFS support */
-	atomic_t nr_wb_bios;			/* # of writeback bios */
 
 	/* # of pages, see count_type */
 	atomic_t nr_pages[NR_COUNT_TYPE];
@@ -1263,7 +1264,8 @@ static inline void inc_page_count(struct f2fs_sb_info *sbi, int count_type)
 {
 	atomic_inc(&sbi->nr_pages[count_type]);
 
-	if (count_type == F2FS_DIRTY_DATA || count_type == F2FS_INMEM_PAGES)
+	if (count_type == F2FS_DIRTY_DATA || count_type == F2FS_INMEM_PAGES ||
+		count_type == F2FS_WB_META || count_type == F2FS_WB_DATA)
 		return;
 
 	set_sbi_flag(sbi, SBI_IS_DIRTY);
@@ -2219,7 +2221,7 @@ struct f2fs_stat_info {
 	unsigned int ndirty_dirs, ndirty_files, ndirty_all;
 	int nats, dirty_nats, sits, dirty_sits, free_nids, alloc_nids;
 	int total_count, utilization;
-	int bg_gc, wb_bios;
+	int bg_gc, nr_wb_meta, nr_wb_data;
 	int inline_xattr, inline_inode, inline_dir, orphans;
 	unsigned int valid_count, valid_node_count, valid_inode_count, discard_blks;
 	unsigned int bimodal, avg_vblocks;
-- 
2.8.2.311.gee88674