f2fs: avoid stucking GC due to atomic write

f2fs doesn't allow abuse on atomic write class interface, so except
limiting in-mem pages' total memory usage capacity, we need to limit
atomic-write usage as well when filesystem is seriously fragmented,
otherwise we may run into infinite loop during foreground GC because
target blocks in victim segment are belong to atomic opened file for
long time.

Now, we will detect failure due to atomic write in foreground GC, if
the count exceeds threshold, we will drop all atomic written data in
cache, by this, I expect it can keep our system running safely to
prevent Dos attack.

In addition, his patch adds to show GC skip information in debugfs,
now it just shows count of skipped caused by atomic write.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
index a66107b5cfff..2d65e77ae5cf 100644
--- a/fs/f2fs/debug.c
+++ b/fs/f2fs/debug.c
@@ -104,6 +104,8 @@ static void update_general_status(struct f2fs_sb_info *sbi)
         si->avail_nids = NM_I(sbi)->available_nids;
         si->alloc_nids = NM_I(sbi)->nid_cnt[PREALLOC_NID];
         si->bg_gc = sbi->bg_gc;
+        si->skipped_atomic_files[BG_GC] = sbi->skipped_atomic_files[BG_GC];
+        si->skipped_atomic_files[FG_GC] = sbi->skipped_atomic_files[FG_GC];
         si->util_free = (int)(free_user_blocks(sbi) >> sbi->log_blocks_per_seg)
                 * 100 / (int)(sbi->user_block_count >> sbi->log_blocks_per_seg)
                 / 2;
@@ -342,6 +344,10 @@ static int stat_show(struct seq_file *s, void *v)
                                 si->bg_data_blks);
                 seq_printf(s, "  - node blocks : %d (%d)\n", si->node_blks,
                                 si->bg_node_blks);
+                seq_printf(s, "Skipped : atomic write %llu (%llu)\n",
+                                si->skipped_atomic_files[BG_GC] +
+                                si->skipped_atomic_files[FG_GC],
+                                si->skipped_atomic_files[BG_GC]);
                 seq_puts(s, "\nExtent Cache:\n");
                 seq_printf(s, "  - Hit Count: L1-1:%llu L1-2:%llu L2:%llu\n",
                                 si->hit_largest, si->hit_cached,