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@kernel.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))
+		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

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@kernel.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?

> +		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

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@kernel.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