linux-kernel - Re: [PATCH] f2fs: fix iostat parameter for discard

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Message-ID: <ddf243c9-f557-7f11-1964-8d2324f84092@kernel.org>
Date:   Tue, 13 Dec 2022 09:46:43 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     Yangtao Li <frank.li@...o.com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: fix iostat parameter for discard

On 2022/12/13 6:59, Jaegeuk Kim wrote:
> On 12/11, Chao Yu wrote:
>> On 2022/12/5 22:56, Yangtao Li wrote:
>>> Just like other data we count uses the number of bytes as the basic unit,
>>> but discard uses the number of cmds as the statistical unit. In fact the
>>> discard command contains the number of blocks, so let's change to the
>>> number of bytes as the base unit.
>>>
>>> Fixes: b0af6d491a6b ("f2fs: add app/fs io stat")
>>>
>>> Signed-off-by: Yangtao Li <frank.li@...o.com>
>>> ---
>>>    fs/f2fs/segment.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index 9486ca49ecb1..bc262e17b279 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -1181,7 +1181,7 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>>>    		atomic_inc(&dcc->issued_discard);
>>> -		f2fs_update_iostat(sbi, NULL, FS_DISCARD, 1);
>>> +		f2fs_update_iostat(sbi, NULL, FS_DISCARD, len * F2FS_BLKSIZE);
>>
>> In order to avoid breaking its usage of application, how about keeping
>> FS_DISCARD as it is, and add FS_DISCARD_IO to account discard bytes?
> 
> I picked this to match the f2fs_update_iostat() definition. Do we know
> how many applications will be affected? I don't have any at a glance in
> Android tho.

I guess there is some private scripts in OEM rely on this, and I don't
see any non-Android users using this.

> 
> void f2fs_update_iostat(struct f2fs_sb_info *sbi, struct inode *inode,
>                          enum iostat_type type, unsigned long long io_bytes)

What do you think of extending this function to support io_counts?

void f2fs_update_iostat(struct f2fs_sb_info *sbi, struct inode *inode,
			enum iostat_type type, unsigned long long io_bytes,
			unsigned long long io_counts)

Thanks,

> 
> 
>>
>> Thanks,
>>
>>>    		lstart += len;
>>>    		start += len;