Re: [PATCH] f2fs: fix to map blocks correctly for direct read

[Chao Yu]

On 2024/11/1 9:22, Jaegeuk Kim wrote:
> On 10/31, Chao Yu wrote:
> > f2fs_map_blocks() supports to map continuous holes or preallocated
> > address, we should avoid setting F2FS_MAP_MAPPED for these cases
> > only, otherwise, it may fail f2fs_iomap_begin(), and make direct
> > write fallbacking to use buffered IO and flush, result in performance
> > regression.
>
> Is this fixing direct write or read?

Direct write.

> > Fixes: 9f0f6bf42714 ("f2fs: support to map continuous holes or preallocated address")
> > Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> > Closes: https://lore.kernel.org/oe-lkp/202409122103.e45aa13b-oliver.sang@xxxxxxxxx
> > Cc: Cyril Hrubis <chrubis@xxxxxxx>
> > Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
> > ---
> >   fs/f2fs/data.c | 7 ++++++-
> >   1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > index 306b86b0595d..38b85160c6bd 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -1676,7 +1676,12 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
> >   		/* reserved delalloc block should be mapped for fiemap. */
> >   		if (blkaddr == NEW_ADDR)
> >   			map->m_flags |= F2FS_MAP_DELALLOC;
> > -		if (flag != F2FS_GET_BLOCK_DIO || !is_hole)
> > +		/*
> > +		 * f2fs_map_blocks() supports to map continuous holes or
> > +		 * preallocated address, don't set F2FS_MAP_MAPPED for these
> > +		 * cases only.
> > +		 */
> > +		if (flag != F2FS_GET_BLOCK_DIO || map->m_may_create || !is_hole)
>
> So, this is adding map->m_may_create, which is for writes?

map->m_may_create is added for write path, w/o this condition, f2fs_map_blocks()
may missed to tag F2FS_MAP_MAPPED, result in that f2fs_iomap_begin() will return
-ENOTBLK.

Am I missing someting?

Thanks,

> >   			map->m_flags |= F2FS_MAP_MAPPED;
> >   
> >   		map->m_pblk = blkaddr;
> > --
> > 2.40.1