linux-kernel - Re: [f2fs-dev] [PATCH v3] f2fs: readahead node blocks in F2FS_GET_BLOCK

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Message-ID: <20250924065338.1359558-1-wangzijie1@honor.com>
Date: Wed, 24 Sep 2025 14:53:38 +0800
From: wangzijie <wangzijie1@...or.com>
To: <linux-f2fs-devel@...ts.sourceforge.net>
CC: <chao@...nel.org>, <jaegeuk@...nel.org>, <linux-kernel@...r.kernel.org>,
	<sj1557.seo@...sung.com>, <yunji0.kang@...sung.com>
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: readahead node blocks in F2FS_GET_BLOCK_PRECACHE mode

>On 9/24/25 13:58, Yunji Kang wrote:
>> In f2fs_precache_extents(), For large files, It requires reading many
>> node blocks. Instead of reading each node block with synchronous I/O,
>> this patch applies readahead so that node blocks can be fetched in
>> advance.
>> 
>> It reduces the overhead of repeated sync reads and improves efficiency
>> when precaching extents of large files.
>> 
>> I created a file with the same largest extent and executed the test.
>> For this experiment, I set the file's largest extent with an offset of 0
>> and a size of 1GB. I configured the remaining area with 100MB extents.
>> 
>> 5GB test file:
>> dd if=/dev/urandom of=test1 bs=1m count=5120
>> cp test1 test2
>> fsync test1
>> dd if=test1 of=test2 bs=1m skip=1024 seek=1024 count=100 conv=notrunc
>> dd if=test1 of=test2 bs=1m skip=1224 seek=1224 count=100 conv=notrunc
>> ...
>> dd if=test1 of=test2 bs=1m skip=5024 seek=5024 count=100 conv=notrunc
>> reboot
>> 
>> I also created 10GB and 20GB files with large extents using the same
>> method.
>> 
>> ioctl(F2FS_IOC_PRECACHE_EXTENTS) test results are as follows:
>>   +-----------+---------+---------+-----------+
>>   | File size | Before  | After   | Reduction |
>>   +-----------+---------+---------+-----------+
>>   | 5GB       | 101.8ms | 37.0ms  | 72.1%     |
>>   | 10GB      | 222.9ms | 56.0ms  | 74.9%     |
>>   | 20GB      | 446.2ms | 116.4ms | 73.9%     |
>>   +-----------+---------+---------+-----------+
>> Tested on a 256GB mobile device with an SM8750 chipset.
>> 
>> Reviewed-by: Sungjong Seo <sj1557.seo@...sung.com>
>> Reviewed-by: Sunmin Jeong <s_min.jeong@...sung.com>
>> Signed-off-by: Yunji Kang <yunji0.kang@...sung.com>
>> ---
>> v2:
>>  - Modify the readahead condition check routine for better code
>> readability.
>>  - Update the title from 'node block' to 'node blocks'.
>> 
>> v3:
>>  - Bug fix to allow more node pages to be readahead.
>>  - Updated with test results.
>> 
>>  fs/f2fs/data.c | 3 +++
>>  fs/f2fs/f2fs.h | 1 +
>>  fs/f2fs/node.c | 4 +++-
>>  3 files changed, 7 insertions(+), 1 deletion(-)
>> 
>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>> index 7961e0ddfca3..ab3117e3b24a 100644
>> --- a/fs/f2fs/data.c
>> +++ b/fs/f2fs/data.c
>> @@ -1572,6 +1572,9 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
>>  	pgofs =	(pgoff_t)map->m_lblk;
>>  	end = pgofs + maxblocks;
>>  
>> +	if (flag == F2FS_GET_BLOCK_PRECACHE)
>> +		mode = LOOKUP_NODE_PRECACHE;
>
>If trigger condition of LOOKUP_NODE_RA and LOOKUP_NODE_PRECACHE is the same,
>What about?
>
>	if (flag == F2FS_GET_BLOCK_PRECACHE)
>		mode = LOOKUP_NODE_RA;
>
>Thanks,

Hi Yunji and Chao,
I think so, we can directly use LOOKUP_NODE_RA for precache extents.
BTW, maybe there are more cases that LOOKUP_NODE_RA will be better? Like
defragment/compress(need to call __f2fs_cluster_blocks() ) ioctl..


>> +
>>  next_dnode:
>>  	if (map->m_may_create) {
>>  		if (f2fs_lfs_mode(sbi))
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> index 9d3bc9633c1d..3ce41528d48e 100644
>> --- a/fs/f2fs/f2fs.h
>> +++ b/fs/f2fs/f2fs.h
>> @@ -651,6 +651,7 @@ enum {
>>  					 * look up a node with readahead called
>>  					 * by get_data_block.
>>  					 */
>> +	LOOKUP_NODE_PRECACHE,		/* look up a node for F2FS_GET_BLOCK_PRECACHE */
>>  };
>>  
>>  #define DEFAULT_RETRY_IO_COUNT	8	/* maximum retry read IO or flush count */
>> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
>> index 4254db453b2d..63e9ee7ab911 100644
>> --- a/fs/f2fs/node.c
>> +++ b/fs/f2fs/node.c
>> @@ -860,7 +860,9 @@ int f2fs_get_dnode_of_data(struct dnode_of_data *dn, pgoff_t index, int mode)
>>  			set_nid(parent, offset[i - 1], nids[i], i == 1);
>>  			f2fs_alloc_nid_done(sbi, nids[i]);
>>  			done = true;
>> -		} else if (mode == LOOKUP_NODE_RA && i == level && level > 1) {
>> +		} else if ((mode == LOOKUP_NODE_RA ||
>> +                (mode == LOOKUP_NODE_PRECACHE))
>> +                && i == level && level > 1) {
>>  			nfolio[i] = f2fs_get_node_folio_ra(parent, offset[i - 1]);
>>  			if (IS_ERR(nfolio[i])) {
>>  				err = PTR_ERR(nfolio[i]);