Tail packing feature on 5.15 Kernel

[Gao Xiang]

Hi Paul,

On Wed, Jul 20, 2022 at 10:38:15PM +0200, Paul Spooren wrote:
> Hi all,
> 
> I’m currently in the process[1] to evaluate erofs as a replacement of squashfs on OpenWrt.
> 
> Since 5.15 will be our next Kernel release but tail packing is only available starting from 5.17, did anyone already do the work of back porting the required patches? If not, could anyone please give me pointers which patches are required?
> 
> Thank you very much for all further advice!

Thanks for your interest.

EROFS is now actively developing so you could see new features
on each new Linux version (I believe many active in-kernel features
behave like this, for example iouring.)

The initial EROFS version was formed as an optimized solution to
compress in 4KiB pcluster so it has minimized memory footprints
and best random performance on Android smartphones, for now the
optimized and recommended configuration is still this one (4KiB,
lz4hc) even though things are quickly changing since recent features
add more possibility but most of these are still quite new and need
to go with the next LTS version (maybe 6.0?).

Also if you'd like to maximize the compression ratio you probably
need `fragments` features which is still under development by Yue
Hu [1].  As I said to you before [2], I still suggest that Openwrt
takes EROFS as an _alternative approach_ instead of a replacement
of Squashfs at least this year since we still need time to optimize
the maximum compression ratio scenarios in addition to 4KiB, lz4hc
(we also need to wait the next stable XZ-utils version first.)

[1] https://lore.kernel.org/r/YpXnhI8gBlSgHEBW@B-P7TQMD6M-0146.local
[2] https://lore.kernel.org/r/cover.1657528899.git.huyue2@coolpad.com

Thanks,
Gao Xiang

> 
> Best,
> Paul
> 
> [1]: https://github.com/openwrt/openwrt/pull/9968