Re: [PATCH v2] f2fs: skip f2fs_preallocate_blocks() for overwrite case

[Chao Yu]

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@xxxxxxxxxx>
> > ---
> > 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