Re: [PATCH 2/5] f2fs: add cur_victim_sec for BG_GC to avoid skipping BG_GC victim

[Yunlong Song <yunlong.song@huawei.com>]

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