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

[Chao Yu <chao@kernel.org>]

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?

	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,