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SubjectRe: [PATCH 2/5] f2fs: add cur_victim_sec for BG_GC to avoid skipping BG_GC victim
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On 2018/7/24 21:11, Chao Yu wrote:
> On 2018/7/23 22:10, Yunlong Song wrote:
>> If f2fs aborts BG_GC, then the section bit of victim_secmap will be set,
>> which will cause the section skipped in the future get_victim of BG_GC.
>> In a worst case that each section in the victim_secmap is set and there
>> are enough free sections (so FG_GC can not be triggered), then BG_GC
>> will skip all the sections and cannot find any victims, causing BG_GC
> If f2fs aborts BG_GC, we'd better to clear victim_secmap?
We can keep the bit set in victim_secmap for FG_GC use next time as
before, the diffierent
is that this patch will make BG_GC ignore the bit set in victim_secmap,
so BG_GC can still
get the the section (which is in set) as victim and do GC jobs.
>
>> failed each time. Besides, SSR also uses BG_GC to get ssr segment, if
> Looks like foreground GC will try to grab section which is selected as
> victim of background GC?
Yes, this is exactly the value of victim_secmap, it helps FG_GC reduce
time in selecting victims
and continue the job which BG_GC has not finished.

>
> Thanks,
>
>> many sections in the victim_secmap are set, then SSR cannot get a proper
>> ssr segment to allocate blocks, which makes SSR inefficiently. To fix
>> this problem, we can add cur_victim_sec for BG_GC similar like that in
>> FG_GC to avoid selecting the same section repeatedly.
>>
>> Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
>> ---
>> fs/f2fs/f2fs.h | 3 ++-
>> fs/f2fs/gc.c | 15 +++++++++------
>> fs/f2fs/segment.h | 3 ++-
>> fs/f2fs/super.c | 3 ++-
>> include/trace/events/f2fs.h | 18 ++++++++++++------
>> 5 files changed, 27 insertions(+), 15 deletions(-)
>>
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> index 57a8851..f8a7b42 100644
>> --- a/fs/f2fs/f2fs.h
>> +++ b/fs/f2fs/f2fs.h
>> @@ -1217,7 +1217,8 @@ struct f2fs_sb_info {
>> /* for cleaning operations */
>> struct mutex gc_mutex; /* mutex for GC */
>> struct f2fs_gc_kthread *gc_thread; /* GC thread */
>> - unsigned int cur_victim_sec; /* current victim section num */
>> + 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 */
>> /* 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 2ba470d..705d419 100644
>> --- a/fs/f2fs/gc.c
>> +++ b/fs/f2fs/gc.c
>> @@ -367,8 +367,6 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
>>
>> if (sec_usage_check(sbi, secno))
>> goto next;
>> - if (gc_type == BG_GC && test_bit(secno, dirty_i->victim_secmap))
>> - goto next;
>>
>> cost = get_gc_cost(sbi, segno, &p);
>>
>> @@ -391,14 +389,17 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
>> if (p.alloc_mode == LFS) {
>> secno = GET_SEC_FROM_SEG(sbi, p.min_segno);
>> if (gc_type == FG_GC)
>> - sbi->cur_victim_sec = secno;
>> - else
>> + sbi->cur_fg_victim_sec = secno;
>> + else {
>> set_bit(secno, dirty_i->victim_secmap);
>> + sbi->cur_bg_victim_sec = secno;
>> + }
>> }
>> *result = (p.min_segno / p.ofs_unit) * p.ofs_unit;
>>
>> trace_f2fs_get_victim(sbi->sb, type, gc_type, &p,
>> - sbi->cur_victim_sec,
>> + sbi->cur_fg_victim_sec,
>> + sbi->cur_bg_victim_sec,
>> prefree_segments(sbi), free_segments(sbi));
>> }
>> out:
>> @@ -1098,7 +1099,9 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
>> }
>>
>> if (gc_type == FG_GC)
>> - sbi->cur_victim_sec = NULL_SEGNO;
>> + sbi->cur_fg_victim_sec = NULL_SEGNO;
>> + else
>> + sbi->cur_bg_victim_sec = NULL_SEGNO;
>>
>> if (!sync) {
>> if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
>> index 5049551..b21bb96 100644
>> --- a/fs/f2fs/segment.h
>> +++ b/fs/f2fs/segment.h
>> @@ -787,7 +787,8 @@ static inline block_t sum_blk_addr(struct f2fs_sb_info *sbi, int base, int type)
>>
>> static inline bool sec_usage_check(struct f2fs_sb_info *sbi, unsigned int secno)
>> {
>> - if (IS_CURSEC(sbi, secno) || (sbi->cur_victim_sec == secno))
>> + if (IS_CURSEC(sbi, secno) || (sbi->cur_fg_victim_sec == secno) ||
>> + (sbi->cur_bg_victim_sec == secno))
>> return true;
>> return false;
>> }
>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>> index 7187885..ef69ebf 100644
>> --- a/fs/f2fs/super.c
>> +++ b/fs/f2fs/super.c
>> @@ -2386,7 +2386,8 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
>> sbi->root_ino_num = le32_to_cpu(raw_super->root_ino);
>> sbi->node_ino_num = le32_to_cpu(raw_super->node_ino);
>> sbi->meta_ino_num = le32_to_cpu(raw_super->meta_ino);
>> - sbi->cur_victim_sec = NULL_SECNO;
>> + sbi->cur_fg_victim_sec = NULL_SECNO;
>> + sbi->cur_bg_victim_sec = NULL_SECNO;
>> sbi->max_victim_search = DEF_MAX_VICTIM_SEARCH;
>>
>> sbi->dir_level = DEF_DIR_LEVEL;
>> diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
>> index 7956989..0f01f82 100644
>> --- a/include/trace/events/f2fs.h
>> +++ b/include/trace/events/f2fs.h
>> @@ -693,10 +693,12 @@
>> TRACE_EVENT(f2fs_get_victim,
>>
>> TP_PROTO(struct super_block *sb, int type, int gc_type,
>> - struct victim_sel_policy *p, unsigned int pre_victim,
>> + struct victim_sel_policy *p, unsigned int pre_fg_victim,
>> + unsigned int pre_bg_victim,
>> unsigned int prefree, unsigned int free),
>>
>> - TP_ARGS(sb, type, gc_type, p, pre_victim, prefree, free),
>> + TP_ARGS(sb, type, gc_type, p, pre_fg_victim, pre_bg_victim,
>> + prefree, free),
>>
>> TP_STRUCT__entry(
>> __field(dev_t, dev)
>> @@ -707,7 +709,8 @@
>> __field(unsigned int, victim)
>> __field(unsigned int, cost)
>> __field(unsigned int, ofs_unit)
>> - __field(unsigned int, pre_victim)
>> + __field(unsigned int, pre_fg_victim)
>> + __field(unsigned int, pre_bg_victim)
>> __field(unsigned int, prefree)
>> __field(unsigned int, free)
>> ),
>> @@ -721,14 +724,16 @@
>> __entry->victim = p->min_segno;
>> __entry->cost = p->min_cost;
>> __entry->ofs_unit = p->ofs_unit;
>> - __entry->pre_victim = pre_victim;
>> + __entry->pre_fg_victim = pre_fg_victim;
>> + __entry->pre_bg_victim = pre_bg_victim;
>> __entry->prefree = prefree;
>> __entry->free = free;
>> ),
>>
>> TP_printk("dev = (%d,%d), type = %s, policy = (%s, %s, %s), "
>> "victim = %u, cost = %u, ofs_unit = %u, "
>> - "pre_victim_secno = %d, prefree = %u, free = %u",
>> + "pre_fg_victim_secno = %d, pre_bg_victim_secno = %d, "
>> + "prefree = %u, free = %u",
>> show_dev(__entry->dev),
>> show_data_type(__entry->type),
>> show_gc_type(__entry->gc_type),
>> @@ -737,7 +742,8 @@
>> __entry->victim,
>> __entry->cost,
>> __entry->ofs_unit,
>> - (int)__entry->pre_victim,
>> + (int)__entry->pre_fg_victim,
>> + (int)__entry->pre_bg_victim,
>> __entry->prefree,
>> __entry->free)
>> );
>>
>
> .
>

--
Thanks,
Yunlong Song


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