On 7/30/25 23:20, Jens Axboe wrote:
> On 7/28/25 2:28 AM, hanqi wrote:
>> ? 2025/7/28 16:07, Chao Yu ??:
>>> On 7/28/25 16:03, hanqi wrote:
>>>> ? 2025/7/28 15:38, Chao Yu ??:
>>>>
>>>>> On 7/25/25 15:53, Qi Han wrote:
>>>>>> Jens has already completed the development of uncached buffered I/O
>>>>>> in git [1], and in f2fs, uncached buffered I/O read can be enabled
>>>>>> simply by setting the FOP_DONTCACHE flag in f2fs_file_operations.
>>>>> IIUC, we may suffer lock issue when we call pwritev(.. ,RWF_DONTCACHE)?
>>>>> as Jen mentioned in below path, right?
>>>>>
>>>>> soft-irq
>>>>> - folio_end_writeback()
>>>>> - filemap_end_dropbehind_write()
>>>>> - filemap_end_dropbehind()
>>>>> - folio_unmap_invalidate()
>>>>> - lock i_lock
>>>>>
>>>>> Thanks,
>>>> That's how I understand it.
>>> So I guess we need to wait for the support RWF_DONTCACHE on write path,
>>> unless
>>> you can walk around for write path in this patch.
>>>
>>> Thanks,
>>
>> I think the read and write paths can be submitted separately.
>> Currently, uncached buffered I/O write requires setting the
>> FGP_DONTCACHE flag when the filesystem allocates a folio. In
>> f2fs, this is done in the following path:
>>
>> - write_begin
>> - f2fs_write_begin
>> - __filemap_get_folio
>> As I understand it, if we don't set the FGP_DONTCACHE flag here, this
>> issue shouldn't occur.
>
> It won't cause an issue, but it also won't work in the sense that the
> intent is that if the file system doesn't support DONTCACHE, it would
> get errored at submission time. Your approach would just ignore the flag
> for writes, rather than return -EOPNOTSUPP as would be expected.
Jens,
Do you mean like what we have done in kiocb_set_rw_flags()?
if (flags & RWF_DONTCACHE) {
/* file system must support it */
if (!(ki->ki_filp->f_op->fop_flags & FOP_DONTCACHE))
return -EOPNOTSUPP;
...
}
IIUC, it's better to have this in original patch, let me know if I'm
missing something.
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 9b8d24097b7a..7f09cad6b6d7 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -5185,6 +5185,11 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb,
struct iov_iter *from)
goto out;
}
+ if (iocb->ki_flags & IOCB_DONTCACHE) {
+ ret = -EOPNOTSUPP;
+ goto out;
+ }
+
if (!f2fs_is_compress_backend_ready(inode)) {
ret = -EOPNOTSUPP;
goto out;
--
Thanks,
>
> You could potentially make it work just on the read side by having the
> f2fs write submit side check DONTCACHE on the write side and error them
> out.
>
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