Re: [f2fs-dev] [PATCH v3] f2fs: readahead node blocks in F2FS_GET_BLOCK_PRECACHE mode

[Chao Yu <chao@kernel.org>]

On 9/24/25 14:53, wangzijie wrote:
>> 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@samsung.com>
>>> Reviewed-by: Sunmin Jeong <s_min.jeong@samsung.com>
>>> Signed-off-by: Yunji Kang <yunji0.kang@samsung.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..

Yeah, we can have a try to check the benefits. :)

Thaks,

> 
> 
>>> +
>>>  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]);