linux-kernel - Re: [PATCH 2/5] f2fs: clear the remaining prefree

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Date:   Fri, 13 Jul 2018 11:28:22 +0800
From:   Yunlong Song <yunlong.song@...wei.com>
To:     Chao Yu <yuchao0@...wei.com>, <jaegeuk@...nel.org>,
        <chao@...nel.org>, <yunlong.song@...oud.com>
CC:     <miaoxie@...wei.com>, <bintian.wang@...wei.com>,
        <shengyong1@...wei.com>, <heyunlei@...wei.com>,
        <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/5] f2fs: clear the remaining prefree_map of the section

round 1: section bitmap : 1 1 1 1 1, all valid, prefree_map: 0 0 0 0 0
then rm data block NO.2, block NO.2 becomes invalid, prefree_map: 0 0 1 0 0
write_checkpoint: section bitmap: 1 1 0 1 1, prefree_map: 0 0 0 0 0, 
prefree of NO.2 is cleared, and no discard issued

round2: rm data block NO.0, NO.1, NO.3, NO.4
all invalid, but prefree bit of NO.2 is set and cleared in round1, then 
prefree_map: 1 1 0 1 1
write_checkpoint: section bitmap: 0 0 0 0 0, prefree_map: 0 0 0 1 1, no 
valid blocks of this section, so discard issued
but this time prefree bit of NO.3 and NO.4 is skipped...

round3:
write_checkpoint: section bitmap: 0 0 0 0 0, prefree_map: 0 0 0 1 1 - > 
0 0 0 0 0, no valid blocks of this section, so discard issued
this time prefree bit of NO.3 and NO.4 is cleared, but the discard of 
this section is sent again...

On 2018/7/13 11:13, Chao Yu wrote:
> On 2018/7/12 23:09, Yunlong Song wrote:
>> For the case when sbi->segs_per_sec > 1, take section:segment = 5 for
>> example, if the section prefree_map is ...previous section | current
>> section (1 1 0 1 1) | next section..., then the start = x, end = x + 1,
>> after start = start_segno + sbi->segs_per_sec, start = x + 5, then it
>> will skip x + 3 and x + 4, but their bitmap is still set, which will
>> cause duplicated f2fs_issue_discard of this same section in the next
>> write_checkpoint, so fix it.
> I didn't get it, if # 2 segment is not prefree state, so it still has valid
> blocks there, so we won't issue discard due to below condition, right?
>
> 		if (!IS_CURSEC(sbi, secno) &&
> 			!get_valid_blocks(sbi, start, true))
>
> Thanks,
>
>> Signed-off-by: Yunlong Song <yunlong.song@...wei.com>
>> ---
>>   fs/f2fs/segment.c | 19 +++++++++++++++++--
>>   1 file changed, 17 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index 47b6595..fd38b61 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -1684,8 +1684,23 @@ void f2fs_clear_prefree_segments(struct f2fs_sb_info *sbi,
>>   		start = start_segno + sbi->segs_per_sec;
>>   		if (start < end)
>>   			goto next;
>> -		else
>> -			end = start - 1;
>> +		else {
>> +			start_segno = start;
>> +
>> +			while (1) {
>> +				start = find_next_bit(prefree_map, start_segno,
>> +									end + 1);
>> +				if (start >= start_segno)
>> +					break;
>> +				end = find_next_zero_bit(prefree_map, start_segno,
>> +										start + 1);
>> +				for (i = start; i < end; i++)
>> +					clear_bit(i, prefree_map);
>> +				dirty_i->nr_dirty[PRE] -= end - start;
>> +			}
>> +
>> +			end = start_segno - 1;
>> +		}
>>   	}
>>   	mutex_unlock(&dirty_i->seglist_lock);
>>   
>>
>
> .
>

-- 
Thanks,
Yunlong Song