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Subject[PATCH 4/5] f2fs: let BG_GC check every dirty segments and gc over a threshold
Date
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.song@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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