Re: [f2fs-dev] [PATCH v2] f2fs: readahead node blocks in F2FS_GET_BLOCK_PRECACHE mode

[Chao Yu via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

On 9/18/25 16:20, 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 | 72.1ms  | 29.2%     |
>   | 10GB      | 222.9ms | 149.5ms | 32.9%     |
>   | 20GB      | 446.2ms | 276.3ms | 38.1%     |
>   +-----------+---------+---------+-----------+

Yunji,

Will we gain better performance if we readahead more node pages w/
sychronous request for precache extent case? Have you tried that?

Thanks,

> 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'.
> 
>  fs/f2fs/data.c | 3 +++
>  fs/f2fs/f2fs.h | 1 +
>  fs/f2fs/node.c | 5 ++++-
>  3 files changed, 8 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;
> +
>  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..d4bf3ce715c5 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -860,7 +860,10 @@ 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 ((i == level && level > 1) &&
> +				(mode == LOOKUP_NODE_RA ||
> +				(mode == LOOKUP_NODE_PRECACHE &&
> +				offset[i - 1] % MAX_RA_NODE == 0))) {
>  			nfolio[i] = f2fs_get_node_folio_ra(parent, offset[i - 1]);
>  			if (IS_ERR(nfolio[i])) {
>  				err = PTR_ERR(nfolio[i]);



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