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

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Message-ID: <fede8a9b-8532-4d63-a4db-b52ed088d6f8@kernel.org>
Date: Fri, 1 Nov 2024 09:32:42 +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 2024/11/1 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@...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.

Am I missing someting?

Thanks,

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