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Message-ID: <dc3d4ca0-7cbb-e856-9f33-da630c6bca59@kernel.org>
Date: Wed, 25 Jul 2018 23:48:49 +0800
From: Chao Yu <chao@...nel.org>
To: Yunlong Song <yunlong.song@...wei.com>,
Chao Yu <yuchao0@...wei.com>, jaegeuk@...nel.org,
yunlong.song@...oud.com
Cc: miaoxie@...wei.com, bintian.wang@...wei.com, shengyong1@...wei.com,
heyunlei@...wei.com, linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] f2fs: add cur_victim_sec for BG_GC to avoid skipping
BG_GC victim
On 2018/7/24 23:19, Yunlong Song wrote:
>
>
> On 2018/7/24 22:17, Chao Yu wrote:
>> On 2018/7/24 21:39, Yunlong Song wrote:
>>>
>>> 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
>> No, I don't think we could assume that FGGC will come soon, and in adaptive
>> mode, after we triggered SSR agressively, FG_GC will be much less.
>>
>> For your case, we need to clear victim_secmap.
> However, if it is cleared, then FG_GC will lose the chance to have a quick
> selection of the victim
> candidate, which BG_GC has selected and aborted in last round or there are still
> some blocks
> ungced because these blocks belong to an opening atomic file. Especially for the
> large section
> case, when BG_GC stops its job if IO state change from idle to busy, then it is
> better that FG_GC
> can continue to gc the section selected before. So how about adding another map
> to record these
> sections, and make FG_GC/BG_GC select these sections, as for the old
> victim_secmap, keep its
> old logic, BG_GC can not select those sections in victim_secmap, but FG_GC can.
Let's discuss optimization ideas on GC offline? it will be fast and direct than
in mailing list. :)
Thanks,
>
>>
>>> 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.
>> I guess this scenario is the case our previous scheme tries to prevent, since if
>> in selected section, all block there are cached and set dirty, BGGC will end up
>> with doing nothing, it's inefficient.
>
> OK, I understand.
>
>>
>> Thanks,
>>
>>>>> 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@...wei.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)
>>>>> );
>>>>>
>>>> .
>>>>
>> .
>>
>
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