Re: [f2fs-dev] [PATCH 4/5] f2fs: do not stop GC when requiring a free section

[Chao Yu <chao@kernel.org>]

On 2022/5/10 0:55, Jaegeuk Kim wrote:
> On 05/08, Chao Yu wrote:
>> On 2022/5/7 7:20, 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>
>>> ---
>>>    fs/f2fs/f2fs.h              |  1 +
>>>    fs/f2fs/file.c              | 12 ++++++++----
>>>    fs/f2fs/gc.c                | 11 +++++++----
>>>    fs/f2fs/segment.c           |  3 ++-
>>>    fs/f2fs/super.c             |  3 ++-
>>>    include/trace/events/f2fs.h | 11 ++++++++---
>>>    6 files changed, 28 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index d49b9b476592..27871f6efb01 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -1282,6 +1282,7 @@ 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 0e7d101c3e65..7072c2b86b2f 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;
>>> @@ -2453,7 +2454,8 @@ 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;
>>> @@ -2494,7 +2496,8 @@ 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;
>>> @@ -2940,7 +2943,8 @@ 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 ec3f6f876e76..f63576ff1c2d 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 init_gc_type is BG_GC, sec_freed won't increase for background GC due to
>> below statement:
>>
>> 		if (gc_type == FG_GC &&
>> 				get_valid_blocks(sbi, segno, false) == 0)
>> 			seg_freed++;
>>
>> It may cause gc thread migrates lots of segments in each round?
> 
> BG_GC include two cases, f2fs_balance_fs and gc thread for GC_MERGE, both of
> which are no_bg_gc=true. So, I think this would be enough. Other cases that sets
> nr_free_secs to 1  should be FG_GC only.

What I mean is, in below check condition, for BG_GC cases,
if !has_not_enough_free_secs(sbi, sec_freed, 0) is true, since sec_freed will
never be increased due to above condition, so it will goto gc_more label all
the time, result in looping until migrating all dirty segments.

Thanks,

> 
>>
>> 	if ((gc_control->init_gc_type == FG_GC ||
>> 			!has_not_enough_free_secs(sbi, sec_freed, 0))) {
>> 		if (sec_freed < gc_control->nr_free_secs)
>> 			goto gc_more;
>> 		goto stop;
>> 	}
>>
>>>    		/* if return value is not zero, no victim was selected */
>>>    		if (f2fs_gc(sbi, &gc_control))
>>> @@ -1776,6 +1777,7 @@ 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),
>>> @@ -1848,11 +1850,12 @@ 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, sec_freed, 0))
>>> +	if ((gc_control->init_gc_type == FG_GC ||
>>> +			!has_not_enough_free_secs(sbi, sec_freed, 0))) {
>>> +		if (sec_freed < gc_control->nr_free_secs)
>>> +			goto gc_more;
>>>    		goto stop;
>>> +	}
>>>    	if (skipped_round <= MAX_SKIP_GC_COUNT || skipped_round * 2 < round) {
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index bc63f0572c64..d6b9231ab0e1 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -528,7 +528,8 @@ 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 };
>>
>> .init_gc_type is BG_GC, so !has_not_enough_free_secs(sbi, sec_freed, 0) condition
>> should be enough to exit?
>>
>> 	if ((gc_control->init_gc_type == FG_GC ||
>> 			!has_not_enough_free_secs(sbi, sec_freed, 0))) {
>> 		if (sec_freed < gc_control->nr_free_secs)
>> 			goto gc_more;
>> 		goto stop;
>> 	}
>>
>> Thanks,
>>
>>>    			f2fs_down_write(&sbi->gc_lock);
>>>    			f2fs_gc(sbi, &gc_control);
>>>    		}
>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>> index 8b23fa6fc6b7..5d5b35067c3d 100644
>>> --- a/fs/f2fs/super.c
>>> +++ b/fs/f2fs/super.c
>>> @@ -2084,7 +2084,8 @@ 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 6699174977a3..349679a72301 100644
>>> --- a/include/trace/events/f2fs.h
>>> +++ b/include/trace/events/f2fs.h
>>> @@ -653,18 +653,21 @@ 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)
>>> @@ -678,6 +681,7 @@ 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;
>>> @@ -687,12 +691,13 @@ 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->no_bg_gc,
>>> +		__entry->nr_free_secs,
>>>    		__entry->dirty_nodes,
>>>    		__entry->dirty_dents,
>>>    		__entry->dirty_imeta,