BG_GC is triggered in idle time, so it is better check every dirty
segment and finds the best victim to gc. Otherwise, BG_GC will be
limited to only 8G areas, and probably select a victim which has nearly
full of valid blocks, resulting a big WAI. Besides, we also add a
bggc_threshold (which is the old "fggc_threshold", so revert commit
"299254") to stop BG_GC when there is no good choice. This is especially
good for large section case to reduce WAI.

Signed-off-by: Yunlong Song <yunlong.s...@huawei.com>
---
 fs/f2fs/f2fs.h    |  2 ++
 fs/f2fs/gc.c      | 23 ++++++++++++++++++++---
 fs/f2fs/segment.h |  9 +++++++++
 3 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index f8a7b42..24a9d7f 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1220,6 +1220,8 @@ struct f2fs_sb_info {
        unsigned int cur_fg_victim_sec;         /* current FG_GC victim section 
num */
        unsigned int cur_bg_victim_sec;         /* current BG_GC victim section 
num */
        unsigned int gc_mode;                   /* current GC state */
+       /* threshold for selecting bg victims */
+       u64 bggc_threshold;
        /* for skip statistic */
        unsigned long long skipped_atomic_files[2];     /* FG_GC and BG_GC */
 
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 0e7a265..21e8d59 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -189,9 +189,8 @@ static void select_policy(struct f2fs_sb_info *sbi, int 
gc_type,
                p->ofs_unit = sbi->segs_per_sec;
        }
 
-       /* we need to check every dirty segments in the FG_GC case */
-       if (gc_type != FG_GC &&
-                       (sbi->gc_mode != GC_URGENT) &&
+       /* we need to check every dirty segments in the GC case */
+       if (p->alloc_mode == SSR &&
                        p->max_search > sbi->max_victim_search)
                p->max_search = sbi->max_victim_search;
 
@@ -230,6 +229,10 @@ 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_bggc_candidate(sbi, secno))
+                       continue;
+
                clear_bit(secno, dirty_i->victim_secmap);
                return GET_SEG_FROM_SEC(sbi, secno);
        }
@@ -368,6 +371,10 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
                if (sec_usage_check(sbi, secno))
                        goto next;
 
+               if (gc_type == BG_GC && p.alloc_mode == LFS &&
+                                       no_bggc_candidate(sbi, secno))
+                       goto next;
+
                cost = get_gc_cost(sbi, segno, &p);
 
                if (p.min_cost > cost) {
@@ -1140,8 +1147,18 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
 
 void f2fs_build_gc_manager(struct f2fs_sb_info *sbi)
 {
+       u64 main_count, resv_count, ovp_count;
+
        DIRTY_I(sbi)->v_ops = &default_v_ops;
 
+       /* threshold of # of valid blocks in a section for victims of BG_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;
+
+       sbi->bggc_threshold = div64_u64((main_count - ovp_count) *
+                                       BLKS_PER_SEC(sbi), (main_count - 
resv_count));
+
        sbi->gc_pin_file_threshold = DEF_GC_FAILED_PINNED_FILES;
 
        /* give warm/cold data area from slower device */
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index b21bb96..932e59b 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -785,6 +785,15 @@ static inline block_t sum_blk_addr(struct f2fs_sb_info 
*sbi, int base, int type)
                                - (base + 1) + type;
 }
 
+static inline bool no_bggc_candidate(struct f2fs_sb_info *sbi,
+                        unsigned int secno)
+{
+    if (get_valid_blocks(sbi, GET_SEG_FROM_SEC(sbi, secno), true) >
+                        sbi->bggc_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_fg_victim_sec == secno) ||
-- 
1.8.5.2


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