Re: [PATCH] f2fs: let __get_victim successfully get a segno in corner case

Yunlong Song <yunlong.song@xxxxxxxxxx> · Mon, 24 Jul 2017 17:18:55 +0800

Hi Jay,
    fggc_threshold is 507, reserved_segment is 462.

On 2017/7/22 5:07, Jaegeuk Kim wrote:
Hi Yunlong,

On 07/20, Yunlong Song wrote:
Hi, Jay,
     The distribution is like this, unit is segment counts:
     cnt_free: 0 (free blocks)
     cnt_full: 25182 (segment which has 512 blocks)
     cnt_over: 25192 (segment which valid blocks over fggc_threshold)
     cnt_below: 870 (segment which valid blocks below fggc_threshold)
What are the values of fggc_threshold and ovp ratio or reserved_segments?
How was the proc/segment_info?

Thanks,

The test is fragment test, add and delete small files over and over.

On 2017/7/18 0:56, Jaegeuk Kim wrote:
On 07/16, sylinux wrote:
In fact，this is not "suppose" case yet, we have already met this problem several times in some test suits for corner case, or I cannot notice that this could happen.
So, have you taken a look at distribution of valid blocks in that case?
I'm wondering what distribution can cause this.

Thanks,



发自网易邮箱大师
On 07/16/2017 09:09, Jaegeuk Kim wrote:
Hi Yunlong,

On 07/14, Yunlong Song wrote:
Suppose that the valid blocks of each section are all over sbi->fggc_threshold,
How about adding a kernel message first to detect your *supposed* sceanrio?
If that happens, it'll be a sort of bug which we haven't assumed.

Thanks,

and even has_not_enough_free_secs is true, f2fs_gc cannot do its job since the
no_fggc_candidate always returns true. As a result, the reserved segments can be
used up, and finally there is no free segment at all, and get_new_segment cannot
get a free segment, filesystem will trap into a wrong status.

To fix this, we record the segno which has a rough minimum cost and return it to
__get_victim to continue f2fs_gc's job.

Signed-off-by: Yunlong Song <yunlong.song@xxxxxxxxxx>
---
  fs/f2fs/gc.c      | 19 ++++++++++++++-----
  fs/f2fs/segment.h | 17 ++++++++++++++---
  2 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index fa3d2e2..965e783 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -178,6 +178,8 @@ static void select_policy(struct f2fs_sb_info *sbi, int gc_type,
          p->offset = 0;
      else
          p->offset = SIT_I(sbi)->last_victim[p->gc_mode];
+
+    p->min_cost_r = UINT_MAX;
  }
  
  static unsigned int get_max_cost(struct f2fs_sb_info *sbi,
@@ -194,7 +196,7 @@ static unsigned int get_max_cost(struct f2fs_sb_info *sbi,
          return 0;
  }
  
-static unsigned int check_bg_victims(struct f2fs_sb_info *sbi)
+static unsigned int check_bg_victims(struct f2fs_sb_info *sbi, struct victim_sel_policy *p)
  {
      struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
      unsigned int secno;
@@ -208,11 +210,12 @@ static unsigned int check_bg_victims(struct f2fs_sb_info *sbi)
          if (sec_usage_check(sbi, secno))
              continue;
  
-        if (no_fggc_candidate(sbi, secno))
+        p->cur_segno_r = GET_SEG_FROM_SEC(sbi, secno);
+        if (no_fggc_candidate(sbi, secno, p))
              continue;
  
          clear_bit(secno, dirty_i->victim_secmap);
-        return GET_SEG_FROM_SEC(sbi, secno);
+        return p->cur_segno_r;
      }
      return NULL_SEGNO;
  }
@@ -332,7 +335,7 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
  
      last_victim = sm->last_victim[p.gc_mode];
      if (p.alloc_mode == LFS && gc_type == FG_GC) {
-        p.min_segno = check_bg_victims(sbi);
+        p.min_segno = check_bg_victims(sbi, &p);
          if (p.min_segno != NULL_SEGNO)
              goto got_it;
      }
@@ -369,8 +372,9 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
              goto next;
          if (gc_type == BG_GC && test_bit(secno, dirty_i->victim_secmap))
              goto next;
+        p.cur_segno_r = segno;
          if (gc_type == FG_GC && p.alloc_mode == LFS &&
-                    no_fggc_candidate(sbi, secno))
+                    no_fggc_candidate(sbi, secno, &p))
              goto next;
  
          cost = get_gc_cost(sbi, segno, &p);
@@ -403,6 +407,11 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
          trace_f2fs_get_victim(sbi->sb, type, gc_type, &p,
                  sbi->cur_victim_sec,
                  prefree_segments(sbi), free_segments(sbi));
+    } else if (has_not_enough_free_secs(sbi, 0, 0)) {
+        p.min_segno = p.min_segno_r;
+        if (p.alloc_mode == LFS && gc_type == FG_GC)
+            clear_bit(GET_SEC_FROM_SEG(sbi, p.min_segno), dirty_i->victim_secmap);
+        goto got_it;
      }
  out:
      mutex_unlock(&dirty_i->seglist_lock);
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 6b871b4..7d2d0f3 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -169,6 +169,9 @@ struct victim_sel_policy {
      unsigned int ofs_unit;        /* bitmap search unit */
      unsigned int min_cost;        /* minimum cost */
      unsigned int min_segno;        /* segment # having min. cost */
+    unsigned int min_cost_r;        /* rough minimum cost */
+    unsigned int min_segno_r;        /* segment # having rough min. cost */
+    unsigned int cur_segno_r;        /* segment # rough process is handling */
  };
  
  struct seg_entry {
@@ -743,11 +746,19 @@ static inline block_t sum_blk_addr(struct f2fs_sb_info *sbi, int base, int type)
  }
  
  static inline bool no_fggc_candidate(struct f2fs_sb_info *sbi,
-                        unsigned int secno)
+                        unsigned int secno, struct victim_sel_policy *p)
  {
-    if (get_valid_blocks(sbi, GET_SEG_FROM_SEC(sbi, secno), true) >=
-                        sbi->fggc_threshold)
+    unsigned int cur_cost;
+
+    cur_cost = get_valid_blocks(sbi, GET_SEG_FROM_SEC(sbi, secno), true);
+    if (cur_cost >= sbi->fggc_threshold) {
+        if (p->min_cost_r > cur_cost) {
+            p->min_cost_r = cur_cost;
+            p->min_segno_r = p->cur_segno_r;
+        }
          return true;
+    }
+
      return false;
  }
  
--
1.8.5.2
.


--
Thanks,
Yunlong Song

.


--
Thanks,
Yunlong Song








