image size on 20.xx builds -- what about a new SMALL target

Stijn Segers foss at
Mon Aug 3 16:17:34 EDT 2020


Op maandag 3 augustus 2020 om 9u40 schreef Henrique de Moraes Holschuh 
<henrique at>:
> On 02/08/2020 19:11, Daniel Golle wrote:
>> 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.

Keep in mind master sets CONFIG_KERNEL_KALLSYMS whereas stable builds 
do not. That alone makes a bit of a size difference (never checked how 
much). Other than that, 5.4 needs more space than 4.14 does (again, how 
much exactly I have not quantified).

Hope this helps a bit.


>> 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]: 
> This sort of commit can easily be a problem even for 8MiB FLASH 
> devices.
> (Some?) vendors are adding a lot of cruft we can't simply jettison 
> from FLASH, e.g. the dual-bootloaders and "http recovery" stuff on 
> TP-Link Archer C60v3 and later, and I understand, several other of 
> their models.
> That effectively reduces usable FLASH enough to matter on 8MiB 
> devices. It is already a problem on OpenWrt 19.07 -- for anything 
> that needs FLASH-filling monsters like OpenSSL and ca-certificates, 
> at least.
> IMO, if things keep going that way (and there is no reason to believe 
> they would not -- or should not, for that matter), we would truly 
> benefit from a SMALL variant soon (not just TINY).  And by soon, I do 
> mean OpenWrt 20.x if at all possible :-(
> Note that I AM NOT speaking against changes that end up increasing 
> core openwrt size.  I am just stating that such changes show the need 
> of one or two knobs for anything that is not possible to build as a 
> "module" kernel-side or as an optional package *and* isn't something 
> you'd strictly need on smaller devices.
> There's TINY, but it removes too much -- being the single true/false 
> knob that exists ATM -- and it seems to be really set up for devices 
> with something like 3-5MiB usable FLASH.  It is also too useful to 
> drop/repurpose, so I am *not* suggesting that.
> A new SMALL could target 5.5MiB to ~6.5MiB *usable* FLASH, IMHO.  One 
> would look at everything that is !TINY to see if it should also be 
> !SMALL, and review for !SMALL what already landed that increases the 
> static kernel size and always-installed package size.
> For not-yet merged changes, you'd ask for !TINY and perhaps !SMALL if 
> they increase in any relevant way the static kernel size, or 
> always-installed package size.  Note that for TINY, 10KiB is already 
> relevant. For !SMALL I am not sure, but I'd say 50KiB as a first try. 
> And exceptional cases would only need a sufficiently good 
> justification in the commit log (as in, enough to convince the core 
> team).
> --
> Henrique de Moraes Holschuh
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