linux-kernel - Re: [f2fs-dev] [PATCH 08/10] f2fs: relax async discard commands more

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Message-ID: <97193665-85ae-268f-c50c-8b29bc4b57c7@huawei.com>
Date:   Fri, 6 Jan 2017 10:06:10 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH 08/10] f2fs: relax async discard commands more

On 2017/1/6 3:46, Jaegeuk Kim wrote:
> On 01/05, Chao Yu wrote:
>> On 2017/1/4 17:29, Chao Yu wrote:
>>> On 2016/12/31 2:51, Jaegeuk Kim wrote:
>>>> This patch relaxes async discard commands to avoid waiting its end_io during
>>>> checkpoint.
>>>> Instead of waiting them during checkpoint, it will be done when actually reusing
>>>> them.
>>>>
>>>> Test on initial partition of nvme drive.
>>>>
>>>>  # time fstrim /mnt/test
>>>>
>>>> Before : 6.158s
>>>> After : 4.822s
>>>>
>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
>>>
>>> Reviewed-by: Chao Yu <yuchao0@...wei.com>
>>>
>>> One comment below,
>>
>> I still have a comment on this patch.
>>
>>>> -void f2fs_wait_all_discard_bio(struct f2fs_sb_info *sbi)
>>>> +/* This should be covered by global mutex, &sit_i->sentry_lock */
>>>> +void f2fs_wait_discard_bio(struct f2fs_sb_info *sbi, unsigned int segno)
>>>>  {
>>>>  	struct list_head *wait_list = &(SM_I(sbi)->wait_list);
>>>>  	struct bio_entry *be, *tmp;
>>>> @@ -646,7 +650,15 @@ void f2fs_wait_all_discard_bio(struct f2fs_sb_info *sbi)
>>>>  		struct bio *bio = be->bio;
>>>>  		int err;
>>>>  
>>>> -		wait_for_completion_io(&be->event);
>>>> +		if (!completion_done(&be->event)) {
>>>> +			if ((be->start_segno >= segno &&
>>>> +					be->end_segno <= segno) ||
>>>
>>> segno >= be->start_segno && segno < be->end_segno ?

Still can not understand this judgment condition, we should wait completion of
discard command only when segno is locate in range of [start_segno, end_segno]?

But now, this condition can be true only when segno, start_segno, end_segno have
equal value.

Please correct me if I'm wrong.

Thanks,

>>
>> Can you check this?
> 
> The be->start_segno and be->end_segno are assigned by:
> 
> unsigned int start_segno = GET_SEGNO(sbi, blkstart);
> unsigned int end_segno = GET_SEGNO(sbi, blkstart + blklen);
> 
> in __f2fs_issue_discard_async().
> 
> So, the problem comes when, for example, blkstart = 0 and blklen = 512.
> 
> I should have got the end_segno by:
> 
> unsigned int end_segno = GET_SEGNO(sbi, blkstart + blklen - 1);
> 
> Thanks,
> 
> .
>