On 02/17, Hou Pengyang wrote:
> On 2017/2/17 7:48, Jaegeuk Kim wrote:
> > Hi Pengyang,
> >
> > Nice
> Hi Jaegeuk,
> catch!
> >
> > I think fggc_threshold needs to be revised, and we need to consider about
> > general victim selection as well.
> >
> > Could you take a look at this?
> >
> > > From 23b265f5ca6405032d092e240c94a827f743e42b Mon Sep 17 00:00:00 2001
> > From: Hou Pengyang <houpengy...@huawei.com>
> > Date: Thu, 16 Feb 2017 12:34:31 +0000
> > Subject: [PATCH] f2fs: add ovp valid_blocks check for bg gc victim to fg_gc
> >
> > For foreground gc, greedy algorithm should be adapted, which makes
> > this formula work well:
> >
> > (2 * (100 / config.overprovision + 1) + 6)
> >
> > But currently, we fg_gc have a prior to select bg_gc victim segments to gc
> > first,
> > these victims are selected by cost-benefit algorithm, we can't guarantee
> > such segments
> > have the small valid blocks, which may destroy the f2fs rule, on the
> > worstest case, would
> > consume all the free segments.
> >
> > This patch fix this by add a filter in check_bg_victims, if segment's has #
> > of valid blocks
> > over overprovision ratio, skip such segments.
> >
> > Cc: <sta...@vger.kernel.org>
> > Signed-off-by: Hou Pengyang <houpengy...@huawei.com>
> > Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org>
> > ---
> > fs/f2fs/f2fs.h | 3 +++
> > fs/f2fs/gc.c | 22 ++++++++++++++++++++--
> > fs/f2fs/segment.h | 9 +++++++++
> > 3 files changed, 32 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index cc22dc458896..1c9f0cc8f027 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -888,6 +888,9 @@ struct f2fs_sb_info {
> > struct f2fs_gc_kthread *gc_thread; /* GC thread */
> > unsigned int cur_victim_sec; /* current victim section num */
> >
> > + /* threshold for converting bg victims for fg */
> > + u64 fggc_threshold;
> > +
> > /* maximum # of trials to find a victim segment for SSR and GC */
> > unsigned int max_victim_search;
> >
> > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > index 88e5e7b10ab6..fd4e479820e6 100644
> > --- a/fs/f2fs/gc.c
> > +++ b/fs/f2fs/gc.c
> > @@ -166,7 +166,8 @@ static void select_policy(struct f2fs_sb_info *sbi, int
> > gc_type,
> > p->ofs_unit = sbi->segs_per_sec;
> > }
> >
> > - if (p->max_search > sbi->max_victim_search)
> > + /* we need to check every dirty segments in the FG_GC case */
> > + if (gc_type != FG_GC && p->max_search > sbi->max_victim_search)
> > p->max_search = sbi->max_victim_search;
> >
> > p->offset = sbi->last_victim[p->gc_mode];
> > @@ -199,6 +200,10 @@ static unsigned int check_bg_victims(struct
> > f2fs_sb_info *sbi)
> > for_each_set_bit(secno, dirty_i->victim_secmap, MAIN_SECS(sbi)) {
> > if (sec_usage_check(sbi, secno))
> > continue;
> > +
> > + if (no_fggc_candidate(sbi, secno))
> > + continue;
> > +
> > clear_bit(secno, dirty_i->victim_secmap);
> > return secno * sbi->segs_per_sec;
> > }
> > @@ -322,13 +327,15 @@ static int get_victim_by_default(struct f2fs_sb_info
> > *sbi,
> > nsearched++;
> > }
> >
> > -
> > secno = GET_SECNO(sbi, segno);
> >
> > if (sec_usage_check(sbi, secno))
> > goto next;
> > if (gc_type == BG_GC && test_bit(secno, dirty_i->victim_secmap))
> > goto next;
> > + if (gc_type == FG_GC && p.alloc_mode == LFS &&
> > + no_fggc_candidate(sbi, secno))
> > + goto next;
> >
> > cost = get_gc_cost(sbi, segno, &p);
> >
> > @@ -989,5 +996,16 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync, bool
> > background)
> >
> > void build_gc_manager(struct f2fs_sb_info *sbi)
> > {
> > + u64 user_block_count, ovp_count, blocks_per_sec, th;
> > +
> > DIRTY_I(sbi)->v_ops = &default_v_ops;
> > +
> > + /* threshold of # of valid blocks in a section for victims of FG_GC */
> > + user_block_count = sbi->user_block_count;
> > + ovp_count = SM_I(sbi)->ovp_segments << sbi->log_blocks_per_seg;
>
> About the ovp_count calculation,
>
> in mkfs.f2fs, we get ovp_segment by
>
> set_cp(overprov_segment_count, (get_sb(segment_count_main) -
> get_cp(rsvd_segment_count)) *
> config.overprovision / 100);
>
> set_cp(overprov_segment_count, get_cp(overprov_segment_count) +
> get_cp(rsvd_segment_count));
>
> where the overprov calculation is based on the space excluding the
> rsvd segment, and the final overprov_segment is sum of the REAL
> overprov segments and the rsvd ones.
>
> So, when to calculate the overprov ratio, the rsvd segments should
> be subtracted from the ckpt->overprov_semgents?
I just got calculation from fresh mounted image. What I could confirm was that
user can see (main_segments - ovp_segments).
BTW, it's worth to verify reserved_segments with that.
>
> Thanks,
>
> > + blocks_per_sec = sbi->blocks_per_seg * sbi->segs_per_sec;
> > +
> > + th = user_block_count * 100 * blocks_per_sec /
> > + ((user_block_count + ovp_count) * 100);
> > + sbi->fggc_threshold = th;
> > }
> > diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> > index 5cb5755c75d9..f4020f141d83 100644
> > --- a/fs/f2fs/segment.h
> > +++ b/fs/f2fs/segment.h
> > @@ -716,6 +716,15 @@ static inline block_t sum_blk_addr(struct f2fs_sb_info
> > *sbi, int base, int type)
> > - (base + 1) + type;
> > }
> >
> > +static inline bool no_fggc_candidate(struct f2fs_sb_info *sbi,
> > + unsigned int secno)
> > +{
> > + if (get_valid_blocks(sbi, secno, sbi->segs_per_sec) >=
> > + sbi->fggc_threshold)
> > + return true;
> > + return false;
> > +}
> > +
> > static inline bool sec_usage_check(struct f2fs_sb_info *sbi, unsigned int
> > secno)
> > {
> > if (IS_CURSEC(sbi, secno) || (sbi->cur_victim_sec == secno))
> >
>
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