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

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Message-ID: <bdc6ecca-d527-4ca8-a476-1c00fcd1ad11@kernel.org>
Date: Sat, 2 Nov 2024 08:25:23 +0800
From: Chao Yu <chao@...nel.org>
To: Jaegeuk Kim <jaegeuk@...nel.org>
Cc: Chao Yu <chao@...nel.org>, 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 2024/11/2 5:06, Jaegeuk Kim wrote:
> 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.

Oops, sorry.

> 
>>
>>>
>>>>
>>>> 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))

More clear, will update w/ this.

Thanks,

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