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

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Message-ID: <ZyVC0R8JYwMZXM9u@google.com>
Date: Fri, 1 Nov 2024 21:06:25 +0000
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao@...nel.org>
Cc: linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	kernel test robot <oliver.sang@...el.com>,
	Cyril Hrubis <chrubis@...e.cz>
Subject: Re: [PATCH] f2fs: fix to map blocks correctly for direct read

On 11/01, Chao Yu wrote:
> 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.

I was confising the patch subject is saying direct read.

> 
> > 
> > > 
> > > Fixes: 9f0f6bf42714 ("f2fs: support to map continuous holes or preallocated address")
> > > Reported-by: kernel test robot <oliver.sang@...el.com>
> > > Closes: https://lore.kernel.org/oe-lkp/202409122103.e45aa13b-oliver.sang@intel.com
> > > Cc: Cyril Hrubis <chrubis@...e.cz>
> > > Signed-off-by: Chao Yu <chao@...nel.org>
> > > ---
> > >   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.

Is that something like this?

/* DIO READ and hole case, should not map the blocks. */
if (!(flag == F2FS_GET_BLOCK_DIO && is_hole && !map->m_may_create))

> 
> Am I missing someting?
> 
> Thanks,
> 
> > 
> > >   			map->m_flags |= F2FS_MAP_MAPPED;
> > >   		map->m_pblk = blkaddr;
> > > -- 
> > > 2.40.1