image size on 20.xx builds

[Daniel Golle]

On Sun, Aug 02, 2020 at 11:49:54PM +0200, Bjoern Franke wrote:
> Hi,
> 
> > 
> > Your Filesystem has a size of 5.81M. MT7620 has a kernel size of around 2M, which exceeds the available space on flash.
> 
> On 19.07.3, the listed lineup of packages has 5.54M and it fits:
> 
> Exportable Squashfs 4.0 filesystem, xz compressed, data block size 262144
> 	compressed data, compressed metadata, compressed fragments,
> 	no xattrs, compressed ids
> 	duplicates are removed
> Filesystem size 5674.78 Kbytes (5.54 Mbytes)
> 	35.35% of uncompressed filesystem size (16051.56 Kbytes)
> Inode table size 13736 bytes (13.41 Kbytes)
> 	22.46% of uncompressed inode table size (61170 bytes)
> Directory table size 17662 bytes (17.25 Kbytes)
> 	44.53% of uncompressed directory table size (39661 bytes)
> 
> 
> 
> > You can try to remove other packages (such as ppp) from the image. Stripping LuCI should also save a lot of space, given you only
> > need it for the initial installation.
> > 
> 
> Yes, but I was wondering why the image gets 300Kb bigger on 20.xx.

Apart from the usual kernel growth we have also enabled a bunch of
previously disabled kernel features on targets which are not marked
as SMALL_FLASH[1]. MT7620 is a mixed bag in that regard and it would
make sense to split it similar to ath79 into a 'tiny' and a 'generic'
variant. The 'mt7620-generic' variant could then also ship with NAND
support and support for Xiami miRouter 3. The 'mt7620-tiny' variant
would have SMALL_FLASH set and hence come without the features
enabled in [1] which should give us ~ 200kB.

[1]: https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=fcb41decf6c622482b20af45a77e62db8d95046e