linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: skip f2fs_preallocate

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Message-ID: <dec765de-407b-07c3-75f6-ec7f71c618b7@kernel.org>
Date:   Fri, 29 Oct 2021 10:34:14 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: skip f2fs_preallocate_blocks() for
 overwrite case

Ping,

On 2021/9/29 8:05, Chao Yu wrote:
> On 2021/9/29 3:08, Jaegeuk Kim wrote:
>> On 09/28, Chao Yu wrote:
>>> In f2fs_file_write_iter(), let's use f2fs_overwrite_io() to
>>> check whethere it is overwrite case, for such case, we can skip
>>> f2fs_preallocate_blocks() in order to avoid f2fs_do_map_lock(),
>>> which may be blocked by checkpoint() potentially.
>>>
>>> Signed-off-by: Chao Yu <chao@...nel.org>
>>> ---
>>>   fs/f2fs/file.c | 4 ++++
>>>   1 file changed, 4 insertions(+)
>>>
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index 13deae03df06..51fecb2f4db5 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -4321,6 +4321,10 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
>>>           preallocated = true;
>>>           target_size = iocb->ki_pos + iov_iter_count(from);
>>> +        if (f2fs_overwrite_io(inode, iocb->ki_pos,
>>> +                        iov_iter_count(from)))
>>> +            goto write;
>>
>> This calls f2fs_map_blocks() which can be duplicate, if it's not the overwirte
>> case. Do we have other benefit?
> 
> f2fs_overwrite_io() will break for append write case w/ below check:
> 
>      if (pos + len > i_size_read(inode))
>          return false;
> 
> I guess we may only suffer double f2fs_map_blocks() for write hole
> case, e.g. truncate to large size & write inside the filesize. For
> this case, how about adding a condition to allow double f2fs_map_blocks()
> only if write size is smaller than a threshold?
> 
> Thanks,
> 
>>
>>> +
>>>           err = f2fs_preallocate_blocks(iocb, from);
>>>           if (err) {
>>>   out_err:
>>> -- 
>>> 2.32.0
> 
> 
> _______________________________________________
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