f2fs: fix to avoid REQ_TIME and CP_TIME collision

Lei Li reported a issue: if foreground operations are frequent, background
checkpoint may be always skipped due to below check, result in losing more
data after sudden power-cut.

f2fs_balance_fs_bg()
...
	if (!is_idle(sbi, REQ_TIME) &&
		(!excess_dirty_nats(sbi) && !excess_dirty_nodes(sbi)))
		return;

E.g:
cp_interval = 5 second
idle_interval = 2 second
foreground operation interval = 1 second (append 1 byte per second into file)

In such case, no matter when it calls f2fs_balance_fs_bg(), is_idle(, REQ_TIME)
returns false, result in skipping background checkpoint.

This patch changes as below to make trigger condition being more reasonable:
- trigger sync_fs() if dirty_{nats,nodes} and prefree segs exceeds threshold;
- skip triggering sync_fs() if there is any background inflight IO or there is
foreground operation recently and meanwhile cp_rwsem is being held by someone;

Reported-by: Lei Li <noctis.akm@gmail.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 13 insertions, 6 deletions

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 273f068e8899..0d25f5ca5618 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -2400,24 +2400,31 @@ static inline void *f2fs_kmem_cache_alloc(struct kmem_cache *cachep,
 	return entry;
 }
 
-static inline bool is_idle(struct f2fs_sb_info *sbi, int type)
+static inline bool is_inflight_io(struct f2fs_sb_info *sbi, int type)
 {
-	if (sbi->gc_mode == GC_URGENT_HIGH)
-		return true;
-
 	if (get_pages(sbi, F2FS_RD_DATA) || get_pages(sbi, F2FS_RD_NODE) ||
 		get_pages(sbi, F2FS_RD_META) || get_pages(sbi, F2FS_WB_DATA) ||
 		get_pages(sbi, F2FS_WB_CP_DATA) ||
 		get_pages(sbi, F2FS_DIO_READ) ||
 		get_pages(sbi, F2FS_DIO_WRITE))
-		return false;
+		return true;
 
 	if (type != DISCARD_TIME && SM_I(sbi) && SM_I(sbi)->dcc_info &&
 			atomic_read(&SM_I(sbi)->dcc_info->queued_discard))
-		return false;
+		return true;
 
 	if (SM_I(sbi) && SM_I(sbi)->fcc_info &&
 			atomic_read(&SM_I(sbi)->fcc_info->queued_flush))
+		return true;
+	return false;
+}
+
+static inline bool is_idle(struct f2fs_sb_info *sbi, int type)
+{
+	if (sbi->gc_mode == GC_URGENT_HIGH)
+		return true;
+
+	if (is_inflight_io(sbi, type))
 		return false;
 
 	if (sbi->gc_mode == GC_URGENT_LOW &&