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Subject[PATCH RFC] f2fs: fix to avoid selecting full segment w/ {AT,}SSR allocator
Date
In cp disabling mode, there could be a condition
- target segment has 128 ckpt valid blocks
- GC migrates 128 valid blocks to other segment (segment is still in
dirty list)
- GC migrates 384 blocks to target segment (segment has 128 cp_vblocks
and 384 vblocks)
- If GC selects target segment via {AT,}SSR allocator, however there is
no free space in targe segment.

Fixes: 4354994f097d ("f2fs: checkpoint disabling")
Fixes: 093749e296e2 ("f2fs: support age threshold based garbage collection")
Signed-off-by: Chao Yu <yuchao0@huawei.com>
---
fs/f2fs/f2fs.h | 1 +
fs/f2fs/gc.c | 17 +++++++++++++----
fs/f2fs/segment.c | 20 ++++++++++++++++++++
3 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index ed7807103c8e..9c753eff0814 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -3376,6 +3376,7 @@ block_t f2fs_get_unusable_blocks(struct f2fs_sb_info *sbi);
int f2fs_disable_cp_again(struct f2fs_sb_info *sbi, block_t unusable);
void f2fs_release_discard_addrs(struct f2fs_sb_info *sbi);
int f2fs_npages_for_summary_flush(struct f2fs_sb_info *sbi, bool for_ra);
+bool segment_has_free_slot(struct f2fs_sb_info *sbi, int segno);
void f2fs_init_inmem_curseg(struct f2fs_sb_info *sbi);
void f2fs_save_inmem_curseg(struct f2fs_sb_info *sbi);
void f2fs_restore_inmem_curseg(struct f2fs_sb_info *sbi);
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 86ba8ed0b8a7..a1d8062cdace 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -392,10 +392,6 @@ static void add_victim_entry(struct f2fs_sb_info *sbi,
if (p->gc_mode == GC_AT &&
get_valid_blocks(sbi, segno, true) == 0)
return;
-
- if (p->alloc_mode == AT_SSR &&
- get_seg_entry(sbi, segno)->ckpt_valid_blocks == 0)
- return;
}

for (i = 0; i < sbi->segs_per_sec; i++)
@@ -736,6 +732,19 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
if (gc_type == BG_GC && test_bit(secno, dirty_i->victim_secmap))
goto next;

+ if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) {
+ /*
+ * to avoid selecting candidate which has below valid
+ * block distribution:
+ * partial blocks are valid and all left ones are valid
+ * in previous checkpoint.
+ */
+ if (p.alloc_mode == SSR || p.alloc_mode == AT_SSR) {
+ if (!segment_has_free_slot(sbi, segno))
+ goto next;
+ }
+ }
+
if (is_atgc) {
add_victim_entry(sbi, &p, segno);
goto next;
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 2d5a82c4ca15..deaf57e13125 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -2650,6 +2650,26 @@ static void __refresh_next_blkoff(struct f2fs_sb_info *sbi,
seg->next_blkoff++;
}

+bool segment_has_free_slot(struct f2fs_sb_info *sbi, int segno)
+{
+ struct sit_info *sit = SIT_I(sbi);
+ struct seg_entry *se = get_seg_entry(sbi, segno);
+ int entries = SIT_VBLOCK_MAP_SIZE / sizeof(unsigned long);
+ unsigned long *target_map = SIT_I(sbi)->tmp_map;
+ unsigned long *ckpt_map = (unsigned long *)se->ckpt_valid_map;
+ unsigned long *cur_map = (unsigned long *)se->cur_valid_map;
+ int i, pos;
+
+ down_write(&sit->sentry_lock);
+ for (i = 0; i < entries; i++)
+ target_map[i] = ckpt_map[i] | cur_map[i];
+
+ pos = __find_rev_next_zero_bit(target_map, sbi->blocks_per_seg, 0);
+ up_write(&sit->sentry_lock);
+
+ return pos < sbi->blocks_per_seg;
+}
+
/*
* This function always allocates a used segment(from dirty seglist) by SSR
* manner, so it should recover the existing segment information of valid blocks
--
2.29.2
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