Re: [RESEND PATCH 0/4] Implement File-Based optimization functionality

[Matias Bjørling]

On 03/11/2022 07.11, Juhyung Park wrote:
...
> Is the idea really an utter madness? Majority of regular files that may 
> be of interest from the perspective of UFS aren't reflinked or 
> snapshotted (let alone the lack of support from ext4 or f2fs).
>
> Device-side fragmentation is a real issue [1] and it makes more than 
> enough sense to defrag LBAs of interests to improve performance. This 
> was long overdue, unless the block interface itself changes somehow.

There are ongoing work with UFS to extend the block interface with 
zones. This approach eliminates the mismatch between the device-side 
mapping and host-side mapping and lets the host and device collaborate 
on the data placement.

> The question is how to implement it correctly without creating a mess 
> with mismatched/outdated LBAs as you've mentioned, preferably through 
> file-system's integration: If the LBAs in questions are indeed 
> reflinked, how do we handle it?, If the LBAs are moved/invalidated from 
> defrag or GC, how do we make sure that UFS is up-to-date?, etc.

If using zoned UFS, the file-system can use zones for LBA tracking, 
eliminating the mismatched/outdated LBA issue. f2fs already supports 
this approach (works today with SMR HDDs and ZNS SSDs). It'll extend to 
UFS when zone support is added/implemented.