linux-kernel - Re: [PATCH v2] f2fs: skip f2fs_preallocate

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Message-ID: <917b4044-80ce-cd46-520b-8325a011631f@kernel.org>
Date:   Tue, 8 Feb 2022 09:41:17 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] f2fs: skip f2fs_preallocate_blocks() for overwrite
 case

On 2022/2/8 3:16, Jaegeuk Kim wrote:
> On 02/04, Chao Yu wrote:
>> There is potential hangtask happened during swapfile's writeback:
>>
>> - loop_kthread_worker_fn		- do_checkpoint
>>    - kthread_worker_fn
>>     - loop_queue_work
>>      - lo_rw_aio
>>       - f2fs_file_write_iter
>>        - f2fs_preallocate_blocks
>>         - f2fs_map_blocks
>> 					 - down_write
>>          - down_read
>>           - rwsem_down_read_slowpath
>>            - schedule
>>
>> One cause is f2fs_preallocate_blocks() will always be called no matter
>> the physical block addresses are allocated or not.
>>
>> This patch tries to check whether block addresses are all allocated with
>> i_size and i_blocks of inode, it's rough because blocks can be allocated
>> beyond i_size, however, we can afford skipping block preallocation in this
>> condition since it's not necessary to do preallocation all the time.
>>
>> Signed-off-by: Chao Yu <chao@...nel.org>
>> ---
>> v2:
>> - check overwrite case with i_size and i_blocks roughly.
>>   fs/f2fs/file.c | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index cfdc41f87f5d..09565d10611d 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -4390,6 +4390,16 @@ static int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *iter,
>>   	int flag;
>>   	int ret;
>>   
>> +	/*
>> +	 * It tries to check whether block addresses are all allocated,
>> +	 * it's rough because blocks can be allocated beyond i_size,
>> +	 * however, we can afford skipping block preallocation since
>> +	 * it's not necessary all the time.
>> +	 */
>> +	if (F2FS_BLK_ALIGN(i_size_read(inode)) ==
>> +			SECTOR_TO_BLOCK(inode->i_blocks))
> 
> Do we count i_blocks only for data?

Oops, it seems it's not...

Needs to introduce another function to calculate node block count based on i_size?

Thanks,

> 
>> +		return 0;
>> +
>>   	/* If it will be an out-of-place direct write, don't bother. */
>>   	if (dio && f2fs_lfs_mode(sbi))
>>   		return 0;
>> -- 
>> 2.32.0