[PATCH RFC] erofs: file-backed mount supports direct io

[Gao Xiang]

On 2025/1/20 11:02, Hongbo Li wrote:
> 
> 

...

>>>   }
>>> +static int erofs_fileio_scan_iter(struct erofs_fileio *io, struct kiocb *iocb,
>>> +                  struct iov_iter *iter)
>>
>> I wonder if it's possible to just extract a folio from
>> `struct iov_iter` and reuse erofs_fileio_scan_folio() logic.
> Thanks for reviewing. Ok, I'll think about reusing the erofs_fileio_scan_folio logic in later version.

Thanks.

> 
> Additionally, for the file-backed mount case, can we consider removing the erofs's page cache and just using the backend file's page cache? If in this way, it will use buffer io for reading the backend's mounted files in default, and it also can decrease the memory overhead.

I think it's too hacky for upstreaming, since EROFS can only
operate its own page cache, otherwise it should only support
overlayfs-like per-inode sharing.

Per-extent sharing among different filesystems is too hacky
on the MM side, but if you have some detailed internal
requirement, you could implement downstream.

Thanks,
Gao Xiang

> 
> This is just my initial idea, for uncompressed mode, this should make sense. But for compressed layout, it needs to be verified.
> 
> Thanks,
> Hongbo
> 
>>
>> It simplifies the codebase a lot, and I think the performance
>> is almost the same.
>>
>> Otherwise currently it looks good to me.
>>
>> Thanks,
>> Gao Xiang