Re: [RFC PATCH v2] mkfs.f2fs: recalculate sit_segments by max_sit_bitmap_size

[Junling Zheng <zhengjunling@huawei.com>]

On 2016/2/23 13:28, Chao Yu wrote:
> Hi all,
> 
>> -----Original Message-----
>> From: Junling Zheng [mailto:zhengjunling@huawei.com]
>> Sent: Tuesday, February 23, 2016 11:47 AM
>> To: linux-f2fs-devel@lists.sourceforge.net; jaegeuk@kernel.org
>> Subject: [f2fs-dev] [RFC PATCH v2] mkfs.f2fs: recalculate sit_segments by max_sit_bitmap_size
>>
>> In most cases, sit_bitmap_size is smaller than MAX_SIT_BITMAP_SIZE.
>>
>> However, in some extreme scenarios, such as 16TB, sit_bitmap_size
>> could be larger than MAX_SIT_BITMAP_SIZE.
>>
>> In this case, we should recalculate the sit_segments through
>> max_sit_bitmap_size to prevent sit_ver_bitmap_bytesize got from
>> segment_count_sit in f2fs_write_check_point_pack() being over
>> MAX_SIT_BITMAP_SIZE.
>>
>> Signed-off-by: Junling Zheng <zhengjunling@huawei.com>
>> ---
>>  mkfs/f2fs_format.c | 23 ++++++++++++++++-------
>>  1 file changed, 16 insertions(+), 7 deletions(-)
>>
>> diff --git a/mkfs/f2fs_format.c b/mkfs/f2fs_format.c
>> index 645c2aa..3a050e0 100644
>> --- a/mkfs/f2fs_format.c
>> +++ b/mkfs/f2fs_format.c
>> @@ -191,6 +191,22 @@ static int f2fs_prepare_super_block(void)
>>
>>  	sit_segments = SEG_ALIGN(blocks_for_sit);
>>
>> +	/*
>> +	 * In most cases, sit_bitmap_size is smaller than MAX_SIT_BITMAP_SIZE.
>> +	 * However, in an extreme scenario(16TB), sit_bitmap_size could be larger
>> +	 * than MAX_SIT_BITMAP_SIZE. Thus, we should recalculate the sit_segments
>> +	 * to prevent sit_ver_bitmap_bytesize got from segment_count_sit in
>> +	 * f2fs_write_check_point_pack() being over MAX_SIT_BITMAP_SIZE.
>> +	 */
>> +	sit_bitmap_size = (sit_segments << log_blks_per_seg) / 8;
>> +
>> +	if (sit_bitmap_size > MAX_SIT_BITMAP_SIZE) {
>> +		max_sit_bitmap_size = MAX_SIT_BITMAP_SIZE;
>> +		sit_segments = max_sit_bitmap_size * 8 >> log_blks_per_seg;
>> +		blocks_for_sit = sit_segments << log_blks_per_seg;
>> +	} else
> 
> Still the minor coding style problem.
> 

Do you mean the "else" also needs {} even though it has only one sentence?

> IMO, maybe it would be better to limit config.total_sectors with 16TB at
> very beginning, so more fields in sb like block_count, segment_count could
> be set correctly when we try to format a huge size image. Right?
> 

Limiting the disk at very beginning means not starting from 0 sector?
Does it amount to reducing the size of disk to keep sit_bitmap_size smaller
than MAX_SIT_BITMAP_SIZE? It looks to be helpful:)

Indeed, the data in sb have no problem. Just the difference of calculating
methods between sit_bitmap_size and MAX_SIT_BITMAP_SIZE:

F2FS_MAX_SEGMENT:
    16 * 1024 * 1024 / 2 = 8388608
max blocks_for_sit:
    ALIGN(F2FS_MAX_SEGMENT, SIT_ENTRY_PER_BLOCK) = 152521	// Upward here, not all blocks are used, some are redundant.
max sit_segments:
    ALIGN(blocks_for_sit, config.blks_per_seg) = 298		// Upward here, not all segments are used, some are redundant.
max segment_count_sit:
    sit_segments * 2 = 596
max sit_ver_bitmap_bytesize:
    ((segment_count_sit / 2) << log_blocks_per_seg) / 8 = 19072	// Here, bitmap size is too large because of the redundant blocks and segments.

However, MAX_SIT_BITMAP_SIZE is defined as:
    ((F2FS_MAX_SEGMENT / SIT_ENTRY_PER_BLOCK) / 8) = 19065	// Downward here, abandon the redundant segments.

So, the best way is to unify the two calculating method:)

Thanks,

> Thanks,
> 
>> +		max_sit_bitmap_size = sit_bitmap_size;
>> +
>>  	set_sb(segment_count_sit, sit_segments * 2);
>>
>>  	set_sb(nat_blkaddr, get_sb(sit_blkaddr) + get_sb(segment_count_sit) *
>> @@ -208,13 +224,6 @@ static int f2fs_prepare_super_block(void)
>>  	 * This number resizes NAT bitmap area in a CP page.
>>  	 * So the threshold is determined not to overflow one CP page
>>  	 */
>> -	sit_bitmap_size = ((get_sb(segment_count_sit) / 2) <<
>> -				log_blks_per_seg) / 8;
>> -
>> -	if (sit_bitmap_size > MAX_SIT_BITMAP_SIZE)
>> -		max_sit_bitmap_size = MAX_SIT_BITMAP_SIZE;
>> -	else
>> -		max_sit_bitmap_size = sit_bitmap_size;
>>
>>  	/*
>>  	 * It should be reserved minimum 1 segment for nat.
>> --
>> 1.9.1
>>
>>
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> 
> 
> .
> 



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