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

[Jaegeuk Kim]

On 07/16, sylinux wrote:
> In factïthis 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,

> 
> 
> 
> 
> åèçæéçåå
> 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