Re: [PATCH RFC v2] mkfs.f2fs: binary decision to calculate SIT/NAT/SSA

[Chao Yu <chao@kernel.org>]

On 2018/1/10 12:01, Gaoxiang (OS) wrote:
> Use binary decision approach to calculate SIT/NAT/SSA segments
> it has some benefits when the partition size >= 512G.
> 
>                         (bsearch)
> psize   main_segments   main_seaments
> ...
> 512G    261509          261510
>  1 T    523141          523143
>  2 T    1046405         1046409
>  4 T    2092783         2092791
> ...
> 
> It also clarify that SIT/NAT/SSA are used for main segment area only.
> 
> Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
> ---
> Change log from v1:
>    - use align_down instead of align_up in get_best_main_zones
> 
>  mkfs/f2fs_format.c | 112 ++++++++++++++++++++++++++++++++++++++---------------
>  1 file changed, 80 insertions(+), 32 deletions(-)
> 
> diff --git a/mkfs/f2fs_format.c b/mkfs/f2fs_format.c
> index a130001..9ca2257 100644
> --- a/mkfs/f2fs_format.c
> +++ b/mkfs/f2fs_format.c
> @@ -145,20 +145,80 @@ static void verify_cur_segs(void)
>  		c.cur_seg[i] = next_zone(i - 1);
>  }
>  
> +static u_int32_t get_best_main_zones(void)
> +{
> +	u_int32_t total_zones = get_sb(segment_count) / (c.segs_per_zone);
> +	u_int32_t left = 1, right = total_zones - 1;
> +	u_int32_t candicate = 0;
> +
> +	while (left <= right) {
> +		u_int32_t blocks_for_nat;
> +		u_int32_t sit_segments, nat_segments, ssa_segments;
> +		u_int32_t meta_segments, meta_zones;
> +		u_int32_t max_sit_bitmap_size, max_nat_bitmap_size;
> +
> +		u_int32_t main_zones = (left + right) / 2;

If we start to search zone size from total_zones/2, it can be a little bit
slow, how about starting from the size that calculated by original method,
and then expanding main zone until founding the target?

Thanks,

> +		u_int32_t main_segments = c.segs_per_zone * main_zones;
> +
> +		sit_segments = SEG_ALIGN(SIZE_ALIGN(main_segments,
> +			SIT_ENTRY_PER_BLOCK) /* blocks_for_sit */);
> +
> +		blocks_for_nat = SIZE_ALIGN(main_segments * c.blks_per_seg,
> +				NAT_ENTRY_PER_BLOCK);
> +
> +		max_sit_bitmap_size = min((u_int32_t)MAX_SIT_BITMAP_SIZE,
> +			sit_segments * c.blks_per_seg / 8);
> +
> +		/*
> +		 * it's weird because for 1TB storage, payload is still not
> +		 * used and max_nat_bitmap_blks is only 21472, which means
> +		 * the total number of nodes is 21472 * 409 = 8782048
> +		 */
> +		if (max_sit_bitmap_size > MAX_SIT_BITMAP_SIZE_IN_CKPT)
> +			max_nat_bitmap_size = CHECKSUM_OFFSET -
> +					sizeof(struct f2fs_checkpoint) + 1;
> +		else
> +			max_nat_bitmap_size =
> +				CHECKSUM_OFFSET - sizeof(struct f2fs_checkpoint) + 1
> +				- max_sit_bitmap_size;
> +
> +		nat_segments = min(SEG_ALIGN(blocks_for_nat),
> +			(max_nat_bitmap_size * 8) / c.blks_per_seg);
> +
> +		/* each main segment has a ssa block */
> +		ssa_segments = SEG_ALIGN(main_segments);
> +
> +		meta_segments = (get_sb(segment_count_ckpt) +
> +			sit_segments * 2 + nat_segments * 2 +
> +			ssa_segments);
> +
> +		meta_zones = ZONE_ALIGN(meta_segments * c.blks_per_seg);
> +
> +		if (meta_zones + main_zones == total_zones)
> +			return main_zones;
> +
> +		if (meta_zones + main_zones < total_zones) {
> +			left = main_zones + 1;
> +			candicate = main_zones;
> +		} else
> +			right = main_zones - 1;
> +	}
> +
> +	return candicate;
> +}
> +
>  static int f2fs_prepare_super_block(void)
>  {
>  	u_int32_t blk_size_bytes;
>  	u_int32_t log_sectorsize, log_sectors_per_block;
>  	u_int32_t log_blocksize, log_blks_per_seg;
>  	u_int32_t segment_size_bytes, zone_size_bytes;
> -	u_int32_t sit_segments;
> -	u_int32_t blocks_for_sit, blocks_for_nat, blocks_for_ssa;
> -	u_int32_t total_valid_blks_available;
> +	u_int32_t blocks_for_sit, blocks_for_nat;
>  	u_int64_t zone_align_start_offset, diff;
>  	u_int64_t total_meta_zones, total_meta_segments;
>  	u_int32_t sit_bitmap_size, max_sit_bitmap_size;
>  	u_int32_t max_nat_bitmap_size, max_nat_segments;
> -	u_int32_t total_zones;
> +	u_int32_t main_zones, main_segments;
>  	u_int32_t next_ino;
>  	enum quota_type qtype;
>  	int i;
> @@ -256,22 +316,18 @@ static int f2fs_prepare_super_block(void)
>  	set_sb(sit_blkaddr, get_sb(segment0_blkaddr) +
>  			get_sb(segment_count_ckpt) * c.blks_per_seg);
>  
> -	blocks_for_sit = SIZE_ALIGN(get_sb(segment_count), SIT_ENTRY_PER_BLOCK);
> +	/* try to do binary decision to get main_zones */
> +	main_zones = get_best_main_zones();
> +	main_segments = c.segs_per_zone * main_zones;
>  
> -	sit_segments = SEG_ALIGN(blocks_for_sit);
> -
> -	set_sb(segment_count_sit, sit_segments * 2);
> +	blocks_for_sit = SIZE_ALIGN(main_segments, SIT_ENTRY_PER_BLOCK);
> +	set_sb(segment_count_sit, SEG_ALIGN(blocks_for_sit) * 2);
>  
>  	set_sb(nat_blkaddr, get_sb(sit_blkaddr) + get_sb(segment_count_sit) *
>  			c.blks_per_seg);
>  
> -	total_valid_blks_available = (get_sb(segment_count) -
> -			(get_sb(segment_count_ckpt) +
> -			get_sb(segment_count_sit))) * c.blks_per_seg;
> -
> -	blocks_for_nat = SIZE_ALIGN(total_valid_blks_available,
> +	blocks_for_nat = SIZE_ALIGN(main_segments * c.blks_per_seg,
>  			NAT_ENTRY_PER_BLOCK);
> -
>  	set_sb(segment_count_nat, SEG_ALIGN(blocks_for_nat));
>  	/*
>  	 * The number of node segments should not be exceeded a "Threshold".
> @@ -312,16 +368,8 @@ static int f2fs_prepare_super_block(void)
>  	set_sb(ssa_blkaddr, get_sb(nat_blkaddr) + get_sb(segment_count_nat) *
>  			c.blks_per_seg);
>  
> -	total_valid_blks_available = (get_sb(segment_count) -
> -			(get_sb(segment_count_ckpt) +
> -			get_sb(segment_count_sit) +
> -			get_sb(segment_count_nat))) *
> -			c.blks_per_seg;
>  
> -	blocks_for_ssa = total_valid_blks_available /
> -				c.blks_per_seg + 1;
> -
> -	set_sb(segment_count_ssa, SEG_ALIGN(blocks_for_ssa));
> +	set_sb(segment_count_ssa, SEG_ALIGN(main_segments));
>  
>  	total_meta_segments = get_sb(segment_count_ckpt) +
>  		get_sb(segment_count_sit) +
> @@ -354,10 +402,7 @@ static int f2fs_prepare_super_block(void)
>  		}
>  	}
>  
> -	total_zones = get_sb(segment_count) / (c.segs_per_zone) -
> -							total_meta_zones;
> -
> -	set_sb(section_count, total_zones * c.secs_per_zone);
> +	set_sb(section_count, main_zones * c.secs_per_zone);
>  
>  	set_sb(segment_count_main, get_sb(section_count) * c.segs_per_sec);
>  
> @@ -373,6 +418,9 @@ static int f2fs_prepare_super_block(void)
>  		return -1;
>  	}
>  
> +	ASSERT((total_meta_zones + main_zones) * c.segs_per_zone
> +		== get_sb(segment_count));
> +
>  	c.reserved_segments =
>  			(2 * (100 / c.overprovision + 1) + 6)
>  			* c.segs_per_sec;
> @@ -404,15 +452,15 @@ static int f2fs_prepare_super_block(void)
>  					qtype, next_ino - 1);
>  	}
>  
> -	if (total_zones <= 6) {
> +	if (main_zones <= 6) {
>  		MSG(1, "\tError: %d zones: Need more zones "
> -			"by shrinking zone size\n", total_zones);
> +			"by shrinking zone size\n", main_zones);
>  		return -1;
>  	}
>  
>  	if (c.heap) {
>  		c.cur_seg[CURSEG_HOT_NODE] =
> -				last_section(last_zone(total_zones));
> +				last_section(last_zone(main_zones));
>  		c.cur_seg[CURSEG_WARM_NODE] = prev_zone(CURSEG_HOT_NODE);
>  		c.cur_seg[CURSEG_COLD_NODE] = prev_zone(CURSEG_WARM_NODE);
>  		c.cur_seg[CURSEG_HOT_DATA] = prev_zone(CURSEG_COLD_NODE);
> @@ -424,10 +472,10 @@ static int f2fs_prepare_super_block(void)
>  		c.cur_seg[CURSEG_COLD_NODE] = next_zone(CURSEG_WARM_NODE);
>  		c.cur_seg[CURSEG_HOT_DATA] = next_zone(CURSEG_COLD_NODE);
>  		c.cur_seg[CURSEG_COLD_DATA] =
> -				max(last_zone((total_zones >> 2)),
> +				max(last_zone((main_zones >> 2)),
>  					next_zone(CURSEG_COLD_NODE));
>  		c.cur_seg[CURSEG_WARM_DATA] =
> -				max(last_zone((total_zones >> 1)),
> +				max(last_zone((main_zones >> 1)),
>  					next_zone(CURSEG_COLD_DATA));
>  	}
>  
> 

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