Re: [PATCH v7 0/3] FDP and per-io hints

Bart Van Assche
2024-10-17T16:15:43Z

On 10/17/24 8:44 AM, Keith Busch wrote:
> On Thu, Oct 17, 2024 at 05:23:37PM +0200, Christoph Hellwig wrote:
>> If you want to do useful stream separation you need to write data
>> sequentially into the stream. Now with streams or FDP that does not
>> actually imply sequentially in LBA space, but if you want the file
>> system to not actually deal with fragmentation from hell, and be
>> easily track what is grouped together you really want it sequentially
>> in the LBA space as well. In other words, any kind of write placement
>> needs to be intimately tied to the file system block allocator.
>
> I'm replying just to make sure I understand what you're saying:
>
> If we send per IO hints on a file, we could have interleaved hot and
> cold pages at various offsets of that file, so the filesystem needs an
> efficient way to allocate extents and track these so that it doesn't
> interleave these in LBA space. I think that makes sense.
>
> We can add a fop_flags and block/fops.c can be the first one to turn it
> on since that LBA access is entirely user driven.

Does anyone care about buffered I/O to block devices? When using
buffered I/O, the write_hint information from the inode is used and the
per I/O write_hint information is ignored.

Thanks,

Bart.