On 9/24/25 12:17, 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,
>>
>
> Does “readahead more node pages” mean removing this condition?
> " offset[i - 1] % MAX_RA_NODE == 0 "
Actually, I meant a) remove "offset[i - 1] % MAX_RA_NODE == 0" or b)
increase MAX_RA_NODE.
Also, maybe we can try as below to trigger synchronous IO for such high
determinacy read.
void df2fs_ra_node_page()
{
...
err = read_node_folio(afolio, 0);
...
}
>
> I originally added the condition to prevent unnecessary readahead requests,
> but it seems this condition was actually blocking valid readahead as well.
>
> After removing the condition and running tests,
> I confirmed that more readahead node pages are being issued.
>
> I’ll share the test results along with the improved patch.
It makes sense, thanks for checking this and sharing the result.
Thanks,
>
> Thanks,
>
>>> Tested on a 256GB mobile device with an SM8750 chipset.
>>>
>>> Reviewed-by: Sungjong Seo <[email protected]>
>>> Reviewed-by: Sunmin Jeong <[email protected]>
>>> Signed-off-by: Yunji Kang <[email protected]>
>>> ---
>>> 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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