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Date:   Tue, 17 May 2022 10:19:25 +0800
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Subject: Re: [f2fs-dev] [PATCH 4/5 v2] f2fs: do not stop GC when requiring a
 free section
Content-Language: en-US
To:     Jaegeuk Kim <jaegeuk@kernel.org>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
References: <20220506232032.1264078-1-jaegeuk@kernel.org>
 <20220506232032.1264078-4-jaegeuk@kernel.org> <Yn1zC6MUZOEbSlWK@google.com>
 <c4a1b40f-469c-8e27-5fef-cd0d3ccd0089@kernel.org>
 <YoKJ4MSoZqVWiYxG@google.com>
From:   Chao Yu <chao@kernel.org>
In-Reply-To: <YoKJ4MSoZqVWiYxG@google.com>
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On 2022/5/17 1:29, Jaegeuk Kim wrote:
> On 05/15, Chao Yu wrote:
>> On 2022/5/13 4:50, Jaegeuk Kim wrote:
>>> The f2fs_gc uses a bitmap to indicate pinned sections, but when disabling
>>> chckpoint, we call f2fs_gc() with NULL_SEGNO which selects the same dirty
>>> segment as a victim all the time, resulting in checkpoint=disable failure,
>>> for example. Let's pick another one, if we fail to collect it.
>>>
>>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
>>> ---
>>>
>>>    Change log from v1:
>>>     - refactor the code path to avoid ambiguous condition like BG_GC/sec_freed
>>>
>>>    fs/f2fs/f2fs.h              |  1 +
>>>    fs/f2fs/file.c              | 12 ++++++++----
>>>    fs/f2fs/gc.c                | 14 +++++++++-----
>>>    fs/f2fs/segment.c           |  3 ++-
>>>    fs/f2fs/super.c             |  3 ++-
>>>    include/trace/events/f2fs.h | 11 ++++++++---
>>>    6 files changed, 30 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index 9920b2d6af8f..492af5b96de1 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -1271,6 +1271,7 @@ struct f2fs_gc_control {
>>>    	bool no_bg_gc;			/* check the space and stop bg_gc */
>>>    	bool should_migrate_blocks;	/* should migrate blocks */
>>>    	bool err_gc_skipped;		/* return EAGAIN if GC skipped */
>>> +	unsigned int nr_free_secs;	/* # of free sections to do GC */
>>>    };
>>>    /* For s_flag in struct f2fs_sb_info */
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index d0547bef0851..216081ea8c81 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -1650,7 +1650,8 @@ static int expand_inode_data(struct inode *inode, loff_t offset,
>>>    	struct f2fs_gc_control gc_control = { .victim_segno = NULL_SEGNO,
>>>    			.init_gc_type = FG_GC,
>>>    			.should_migrate_blocks = false,
>>> -			.err_gc_skipped = true };
>>> +			.err_gc_skipped = true,
>>> +			.nr_free_secs = 0 };
>>>    	pgoff_t pg_start, pg_end;
>>>    	loff_t new_size = i_size_read(inode);
>>>    	loff_t off_end;
>>> @@ -2350,7 +2351,8 @@ static int f2fs_ioc_gc(struct file *filp, unsigned long arg)
>>>    	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>>>    	struct f2fs_gc_control gc_control = { .victim_segno = NULL_SEGNO,
>>>    			.no_bg_gc = false,
>>> -			.should_migrate_blocks = false };
>>> +			.should_migrate_blocks = false,
>>> +			.nr_free_secs = 0 };
>>>    	__u32 sync;
>>>    	int ret;
>>> @@ -2391,7 +2393,8 @@ static int __f2fs_ioc_gc_range(struct file *filp, struct f2fs_gc_range *range)
>>>    			.init_gc_type = range->sync ? FG_GC : BG_GC,
>>>    			.no_bg_gc = false,
>>>    			.should_migrate_blocks = false,
>>> -			.err_gc_skipped = range->sync };
>>> +			.err_gc_skipped = range->sync,
>>> +			.nr_free_secs = 0 };
>>>    	u64 end;
>>>    	int ret;
>>> @@ -2837,7 +2840,8 @@ static int f2fs_ioc_flush_device(struct file *filp, unsigned long arg)
>>>    	struct f2fs_gc_control gc_control = {
>>>    			.init_gc_type = FG_GC,
>>>    			.should_migrate_blocks = true,
>>> -			.err_gc_skipped = true };
>>> +			.err_gc_skipped = true,
>>> +			.nr_free_secs = 0 };
>>>    	int ret;
>>>    	if (!capable(CAP_SYS_ADMIN))
>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>> index e275b72bc65f..10b24b0f13a5 100644
>>> --- a/fs/f2fs/gc.c
>>> +++ b/fs/f2fs/gc.c
>>> @@ -147,6 +147,7 @@ static int gc_thread_func(void *data)
>>>    		gc_control.init_gc_type = sync_mode ? FG_GC : BG_GC;
>>>    		gc_control.no_bg_gc = foreground;
>>> +		gc_control.nr_free_secs = foreground ? 1 : 0;
>>>    		/* if return value is not zero, no victim was selected */
>>>    		if (f2fs_gc(sbi, &gc_control))
>>> @@ -1761,6 +1762,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
>>>    	unsigned int skipped_round = 0, round = 0;
>>>    	trace_f2fs_gc_begin(sbi->sb, gc_type, gc_control->no_bg_gc,
>>> +				gc_control->nr_free_secs,
>>>    				get_pages(sbi, F2FS_DIRTY_NODES),
>>>    				get_pages(sbi, F2FS_DIRTY_DENTS),
>>>    				get_pages(sbi, F2FS_DIRTY_IMETA),
>>> @@ -1823,12 +1825,13 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
>>>    	if (gc_type == FG_GC)
>>>    		sbi->cur_victim_sec = NULL_SEGNO;
>>> -	if (gc_control->init_gc_type == FG_GC)
>>> -		goto stop;
>>> -
>>> -	if (!has_not_enough_free_secs(sbi,
>>> -			(gc_type == FG_GC) ? sec_freed : 0, 0))
>>> +	if (gc_control->init_gc_type == FG_GC ||
>>> +	    !has_not_enough_free_secs(sbi,
>>> +				(gc_type == FG_GC) ? sec_freed : 0, 0)) {
>>
>> In all gc_control->init_gc_type = BG_GC cases, gc_control->no_bg_gc is true,
>> if gc_type = BG_GC, then it should break out due to below condition.
>>
>> 	/* f2fs_balance_fs doesn't need to do BG_GC in critical path. */
>> 	if (gc_type == BG_GC && gc_control->no_bg_gc) {
>> 		ret = -EINVAL;
>> 		goto stop;
>> 	}
>>
>> Otherwise gc_type should always be FG_GC in
>> !has_not_enough_free_secs(sbi, (gc_type == FG_GC) ? sec_freed : 0, 0), right?
> 
> We can have gc_type=BG_GC and gc_control->no_bg_gc=false, which is a normal
> background GC path.

Okay, actually if gc_type = BG_GC, sec_freed should be zero at the most time.

Looks fine to me.

Reviewed-by: Chao Yu <chao@kernel.org>

Thanks,

> 
>>
>> Thanks,
>>
>>> +		if (gc_mode == FG_GC && sec_freed < gc_control->nr_free_secs)
>>> +			goto go_gc_more;
>>>    		goto stop;
>>> +	}
>>>    	/* FG_GC stops GC by skip_count */
>>>    	if (gc_type == FG_GC) {
>>> @@ -1849,6 +1852,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
>>>    		if (ret)
>>>    			goto stop;
>>>    	}
>>> +go_gc_more:
>>>    	segno = NULL_SEGNO;
>>>    	goto gc_more;
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index 8b4f2b1d2cca..0a4180f64291 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -404,7 +404,8 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
>>>    				.init_gc_type = BG_GC,
>>>    				.no_bg_gc = true,
>>>    				.should_migrate_blocks = false,
>>> -				.err_gc_skipped = false };
>>> +				.err_gc_skipped = false,
>>> +				.nr_free_secs = 1 };
>>>    			f2fs_down_write(&sbi->gc_lock);
>>>    			f2fs_gc(sbi, &gc_control);
>>>    		}
>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>> index a28c27eed6d0..63daae67a9d9 100644
>>> --- a/fs/f2fs/super.c
>>> +++ b/fs/f2fs/super.c
>>> @@ -2080,7 +2080,8 @@ static int f2fs_disable_checkpoint(struct f2fs_sb_info *sbi)
>>>    			.victim_segno = NULL_SEGNO,
>>>    			.init_gc_type = FG_GC,
>>>    			.should_migrate_blocks = false,
>>> -			.err_gc_skipped = true };
>>> +			.err_gc_skipped = true,
>>> +			.nr_free_secs = 1 };
>>>    		f2fs_down_write(&sbi->gc_lock);
>>>    		err = f2fs_gc(sbi, &gc_control);
>>> diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
>>> index 54ec9e543f09..16c67ede85b6 100644
>>> --- a/include/trace/events/f2fs.h
>>> +++ b/include/trace/events/f2fs.h
>>> @@ -645,18 +645,21 @@ TRACE_EVENT(f2fs_background_gc,
>>>    TRACE_EVENT(f2fs_gc_begin,
>>>    	TP_PROTO(struct super_block *sb, int gc_type, bool no_bg_gc,
>>> +			unsigned int nr_free_secs,
>>>    			long long dirty_nodes, long long dirty_dents,
>>>    			long long dirty_imeta, unsigned int free_sec,
>>>    			unsigned int free_seg, int reserved_seg,
>>>    			unsigned int prefree_seg),
>>> -	TP_ARGS(sb, gc_type, no_bg_gc, dirty_nodes, dirty_dents, dirty_imeta,
>>> +	TP_ARGS(sb, gc_type, no_bg_gc, nr_free_secs, dirty_nodes,
>>> +		dirty_dents, dirty_imeta,
>>>    		free_sec, free_seg, reserved_seg, prefree_seg),
>>>    	TP_STRUCT__entry(
>>>    		__field(dev_t,		dev)
>>>    		__field(int,		gc_type)
>>>    		__field(bool,		no_bg_gc)
>>> +		__field(unsigned int,	nr_free_secs)
>>>    		__field(long long,	dirty_nodes)
>>>    		__field(long long,	dirty_dents)
>>>    		__field(long long,	dirty_imeta)
>>> @@ -670,6 +673,7 @@ TRACE_EVENT(f2fs_gc_begin,
>>>    		__entry->dev		= sb->s_dev;
>>>    		__entry->gc_type	= gc_type;
>>>    		__entry->no_bg_gc	= no_bg_gc;
>>> +		__entry->nr_free_secs	= nr_free_secs;
>>>    		__entry->dirty_nodes	= dirty_nodes;
>>>    		__entry->dirty_dents	= dirty_dents;
>>>    		__entry->dirty_imeta	= dirty_imeta;
>>> @@ -679,12 +683,13 @@ TRACE_EVENT(f2fs_gc_begin,
>>>    		__entry->prefree_seg	= prefree_seg;
>>>    	),
>>> -	TP_printk("dev = (%d,%d), gc_type = %s, no_background_GC = %d, nodes = %lld, "
>>> -		"dents = %lld, imeta = %lld, free_sec:%u, free_seg:%u, "
>>> +	TP_printk("dev = (%d,%d), gc_type = %s, no_background_GC = %d, nr_free_secs = %u, "
>>> +		"nodes = %lld, dents = %lld, imeta = %lld, free_sec:%u, free_seg:%u, "
>>>    		"rsv_seg:%d, prefree_seg:%u",
>>>    		show_dev(__entry->dev),
>>>    		show_gc_type(__entry->gc_type),
>>>    		(__entry->gc_type == BG_GC) ? __entry->no_bg_gc : -1,
>>> +		__entry->nr_free_secs,
>>>    		__entry->dirty_nodes,
>>>    		__entry->dirty_dents,
>>>    		__entry->dirty_imeta,