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Subject: Re: [PATCH RFC 2/5] f2fs: record average update time of segment
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     <linux-f2fs-devel@lists.sourceforge.net>,
        <linux-kernel@vger.kernel.org>, <chao@kernel.org>
References: <20200630100428.19105-1-yuchao0@huawei.com>
 <20200630100428.19105-2-yuchao0@huawei.com>
 <20200701161927.GD1724572@google.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <70776961-0430-0a9f-cf26-09a2cc192b07@huawei.com>
Date:   Fri, 3 Jul 2020 10:13:17 +0800
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On 2020/7/2 0:19, Jaegeuk Kim wrote:
> On 06/30, Chao Yu wrote:
>> Previously, once we update one block in segment, we will update mtime of
>> segment to last time, making aged segment becoming freshest, result in
>> that GC with cost benefit algorithm missing such segment, So this patch
>> changes to record mtime as average block updating time instead of last
>> updating time.
>>
>> It's not needed to reset mtime for prefree segment, as se->valid_blocks
>> is zero, then old se->mtime won't take any weight with below calculation:
>>
>> 	se->mtime = (se->mtime * se->valid_blocks + mtime) /
>> 				(se->valid_blocks + 1);
>>
>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>> ---
>>  fs/f2fs/segment.c | 21 ++++++++++++++++++---
>>  1 file changed, 18 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index 863ec6f1fb87..906c313835ad 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -2150,6 +2150,22 @@ static void __set_sit_entry_type(struct f2fs_sb_info *sbi, int type,
>>  		__mark_sit_entry_dirty(sbi, segno);
>>  }
>>  
>> +static void update_segment_mtime(struct f2fs_sb_info *sbi, block_t blkaddr)
>> +{
>> +	unsigned int segno = GET_SEGNO(sbi, blkaddr);
>> +	struct seg_entry *se = get_seg_entry(sbi, segno);
>> +	unsigned long long mtime = get_mtime(sbi, false);
>> +
>> +	if (!se->mtime) {
> 
> Don't need {}.

Updated,

BTW, have fixed below compile error:

   m68k-linux-ld: fs/f2fs/segment.o: in function `update_segment_mtime':
   fs/f2fs/segment.c:2162: undefined reference to `__udivdi3'

Thanks,

> 
>> +		se->mtime = mtime;
>> +	} else {
>> +		se->mtime = (se->mtime * se->valid_blocks + mtime) /
>> +						(se->valid_blocks + 1);
>> +	}
>> +	if (mtime > SIT_I(sbi)->max_mtime)
>> +		SIT_I(sbi)->max_mtime = mtime;
>> +}
>> +
>>  static void update_sit_entry(struct f2fs_sb_info *sbi, block_t blkaddr, int del)
>>  {
>>  	struct seg_entry *se;
>> @@ -2169,10 +2185,9 @@ static void update_sit_entry(struct f2fs_sb_info *sbi, block_t blkaddr, int del)
>>  	f2fs_bug_on(sbi, (new_vblocks >> (sizeof(unsigned short) << 3) ||
>>  				(new_vblocks > sbi->blocks_per_seg)));
>>  
>> +	update_segment_mtime(sbi, blkaddr);
>> +
>>  	se->valid_blocks = new_vblocks;
>> -	se->mtime = get_mtime(sbi, false);
>> -	if (se->mtime > SIT_I(sbi)->max_mtime)
>> -		SIT_I(sbi)->max_mtime = se->mtime;
>>  
>>  	/* Update valid block bitmap */
>>  	if (del > 0) {
>> -- 
>> 2.26.2
> .
>