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>

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 273f068..0d25f5c 100644 (file)
--- 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 &&

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 1596502..d9e2e65 100644 (file)
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -529,31 +529,38 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi, bool from_bg)
        else
                f2fs_build_free_nids(sbi, false, false);
 
-       if (!is_idle(sbi, REQ_TIME) &&
-               (!excess_dirty_nats(sbi) && !excess_dirty_nodes(sbi)))
+       if (excess_dirty_nats(sbi) || excess_dirty_nodes(sbi) ||
+               excess_prefree_segs(sbi))
+               goto do_sync;
+
+       /* there is background inflight IO or foreground operation recently */
+       if (is_inflight_io(sbi, REQ_TIME) ||
+               (!f2fs_time_over(sbi, REQ_TIME) && rwsem_is_locked(&sbi->cp_rwsem)))
                return;
 
+       /* exceed periodical checkpoint timeout threshold */
+       if (f2fs_time_over(sbi, CP_TIME))
+               goto do_sync;
+
        /* checkpoint is the only way to shrink partial cached entries */
-       if (!f2fs_available_free_memory(sbi, NAT_ENTRIES) ||
-                       !f2fs_available_free_memory(sbi, INO_ENTRIES) ||
-                       excess_prefree_segs(sbi) ||
-                       excess_dirty_nats(sbi) ||
-                       excess_dirty_nodes(sbi) ||
-                       f2fs_time_over(sbi, CP_TIME)) {
-               if (test_opt(sbi, DATA_FLUSH) && from_bg) {
-                       struct blk_plug plug;
-
-                       mutex_lock(&sbi->flush_lock);
-
-                       blk_start_plug(&plug);
-                       f2fs_sync_dirty_inodes(sbi, FILE_INODE);
-                       blk_finish_plug(&plug);
+       if (f2fs_available_free_memory(sbi, NAT_ENTRIES) ||
+               f2fs_available_free_memory(sbi, INO_ENTRIES))
+               return;
 
-                       mutex_unlock(&sbi->flush_lock);
-               }
-               f2fs_sync_fs(sbi->sb, true);
-               stat_inc_bg_cp_count(sbi->stat_info);
+do_sync:
+       if (test_opt(sbi, DATA_FLUSH) && from_bg) {
+               struct blk_plug plug;
+
+               mutex_lock(&sbi->flush_lock);
+
+               blk_start_plug(&plug);
+               f2fs_sync_dirty_inodes(sbi, FILE_INODE);
+               blk_finish_plug(&plug);
+
+               mutex_unlock(&sbi->flush_lock);
        }
+       f2fs_sync_fs(sbi->sb, true);
+       stat_inc_bg_cp_count(sbi->stat_info);
 }
 
 static int __submit_flush_wait(struct f2fs_sb_info *sbi,