f2fs: reclaim prefree segments periodically

Previously, f2fs postpones reclaiming prefree segments into free segments
as much as possible.
However, if user writes and deletes a bunch of data without any sync or fsync
calls, some flash storages can suffer from garbage collections.

So, this patch adds the reclaiming codes to f2fs_write_node_pages and background
GC thread.

If there are a lot of prefree segments, let's do checkpoint so that f2fs
submits discard commands for the prefree regions to the flash storage.

Signed-off-by: Changman Lee <cm224.lee@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

5 files changed, 18 insertions, 1 deletions

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index e8f3fd345ca3..6dff777cd94a 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -299,6 +299,9 @@ struct f2fs_sm_info {
         unsigned int main_segments;     /* # of segments in main area */
         unsigned int reserved_segments; /* # of reserved segments */
         unsigned int ovp_segments;      /* # of overprovision segments */
+
+        /* a threshold to reclaim prefree segments */
+        unsigned int rec_prefree_segments;
 };
 
 /*
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index cb286d7b02b2..783c6cc6253c 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -82,6 +82,11 @@ static int gc_thread_func(void *data)
                 /* if return value is not zero, no victim was selected */
                 if (f2fs_gc(sbi))
                         wait_ms = gc_th->no_gc_sleep_time;
+
+                /* balancing prefree segments */
+                if (excess_prefree_segs(sbi))
+                        f2fs_sync_fs(sbi->sb, true);
+
         } while (!kthread_should_stop());
         return 0;
 }
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index cc119b65a0d3..89dd8a5a3ca3 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -1206,7 +1206,8 @@ static int f2fs_write_node_pages(struct address_space *mapping,
         long nr_to_write = wbc->nr_to_write;
 
         /* First check balancing cached NAT entries */
-        if (try_to_free_nats(sbi, NAT_ENTRY_PER_BLOCK)) {
+        if (try_to_free_nats(sbi, NAT_ENTRY_PER_BLOCK) ||
+                                excess_prefree_segs(sbi)) {
                 f2fs_sync_fs(sbi->sb, true);
                 return 0;
         }
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 177a33b16b2c..62b52f2f293a 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1645,6 +1645,7 @@ int build_segment_manager(struct f2fs_sb_info *sbi)
         sm_info->ovp_segments = le32_to_cpu(ckpt->overprov_segment_count);
         sm_info->main_segments = le32_to_cpu(raw_super->segment_count_main);
         sm_info->ssa_blkaddr = le32_to_cpu(raw_super->ssa_blkaddr);
+        sm_info->rec_prefree_segments = DEF_RECLAIM_PREFREE_SEGMENTS;
 
         err = build_sit_info(sbi);
         if (err)
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 7f94d78cda3d..abe7094c4f7a 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -14,6 +14,8 @@
 #define NULL_SEGNO                      ((unsigned int)(~0))
 #define NULL_SECNO                      ((unsigned int)(~0))
 
+#define DEF_RECLAIM_PREFREE_SEGMENTS    100     /* 200MB of prefree segments */
+
 /* L: Logical segment # in volume, R: Relative segment # in main area */
 #define GET_L2R_SEGNO(free_i, segno)    (segno - free_i->start_segno)
 #define GET_R2L_SEGNO(free_i, segno)    (segno + free_i->start_segno)
@@ -472,6 +474,11 @@ static inline bool has_not_enough_free_secs(struct f2fs_sb_info *sbi, int freed)
                                                 reserved_sections(sbi)));
 }
 
+static inline bool excess_prefree_segs(struct f2fs_sb_info *sbi)
+{
+        return (prefree_segments(sbi) > SM_I(sbi)->rec_prefree_segments);
+}
+
 static inline int utilization(struct f2fs_sb_info *sbi)
 {
         return div_u64((u64)valid_user_blocks(sbi) * 100, sbi->user_block_count);