[PATCH 3.16 161/212] f2fs: add ovp valid_blocks check for bg gc victim to fg_gc

[Ben Hutchings]

3.16.44-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Hou Pengyang <houpengyang@xxxxxxxxxx>

commit e93b9865251a0503d83fd570e7d5a7c8bc351715 upstream.

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.

Signed-off-by: Hou Pengyang <houpengyang@xxxxxxxxxx>
Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>
Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
[bwh: Backported to 3.16:
 - In get_victim_by_default(), use continue rather than goto
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/f2fs/f2fs.h    |  3 +++
 fs/f2fs/gc.c      | 22 ++++++++++++++++++++--
 fs/f2fs/segment.h |  9 +++++++++
 3 files changed, 32 insertions(+), 2 deletions(-)

--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -489,6 +489,9 @@ 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;
 
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -163,7 +163,8 @@ static void select_policy(struct f2fs_sb
 		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];
@@ -196,6 +197,10 @@ static unsigned int check_bg_victims(str
 	for_each_set_bit(secno, dirty_i->victim_secmap, TOTAL_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;
 	}
@@ -302,6 +307,9 @@ static int get_victim_by_default(struct
 			continue;
 		if (gc_type == BG_GC && test_bit(secno, dirty_i->victim_secmap))
 			continue;
+		if (gc_type == FG_GC && p.alloc_mode == LFS &&
+					no_fggc_candidate(sbi, secno))
+			continue;
 
 		cost = get_gc_cost(sbi, segno, &p);
 
@@ -733,7 +741,18 @@ stop:
 
 void build_gc_manager(struct f2fs_sb_info *sbi)
 {
+	u64 main_count, resv_count, ovp_count, blocks_per_sec;
+
 	DIRTY_I(sbi)->v_ops = &default_v_ops;
+
+	/* threshold of # of valid blocks in a section for victims of FG_GC */
+	main_count = SM_I(sbi)->main_segments << sbi->log_blocks_per_seg;
+	resv_count = SM_I(sbi)->reserved_segments << sbi->log_blocks_per_seg;
+	ovp_count = SM_I(sbi)->ovp_segments << sbi->log_blocks_per_seg;
+	blocks_per_sec = sbi->blocks_per_seg * sbi->segs_per_sec;
+
+	sbi->fggc_threshold = div_u64((main_count - ovp_count) * blocks_per_sec,
+					(main_count - resv_count));
 }
 
 int __init create_gc_caches(void)
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -651,6 +651,15 @@ static inline block_t sum_blk_addr(struc
 				- (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))