Hello,
as I mentioned in my previous message (the request for pull request ;-)
), I noticed flash (program memory) usage increase that happened over
last few months.
I bisected the source code and it pointed at commit
6ed4ea63d8168be30227415ea85ae936ca41bb6f . It adds new parameter to
mm_initialize_heap (renamed from mm_initialize.) Further investigation
showed that the program size increase is caused by the new branch (heap
!= NULL). I verified this by forcing the variable to be NULL, the branch
was optimized away and linker eliminated mm_memalign and mm_shrinkchunk
from the resulting binary - yielding 1400 bytes of reduced size. This
matched the increase I spotted.
I work with 8bit microcontroller with 128kB program flash, so 1400 bytes
is not an insignificant amount.
I then went to analyze how is this function called, I found these
occurences:
1. drivers/rptun/rptun.c - called with heap parameter set
2. inline function mm_initialize - heap set to NULL
Other than that, mm_initialize_heap is not called directly. Indirectly,
it is either called from mm_initialize_pool, or it replaces this
function via #define (mm_initialize_pool translated to
mm_initialize_heap)
Considering this, I also analyzed how mm_initialize_pool is called, I
found:
1. multiple occurrences in various functions in mm/ directory. These
either call mm_initialize_heap with heap set to NULL, or pass whatever
was given to them through
2. fs/fs_heap.c - sets heap parameter to NULL
3. drivers/pci/pci_epc.c - is not using config parameter at all, instead
it passes four parameters so it was probably not converted when the
interface changed?
(As a side note - this is the second time this week where I found a
change authored or co-authored by Xiaomi that alters some internal
interface and then converts users of that interface... except some.
Seemingly missing are the ones that are fairly recent additions - the
other one is AVR DA/DB subarchitecture which currently fails to build
with default configuration; proposed fix is in my previous message.
Are they/are you working on some outdated fork of NuttX upstream? Even
more curious is that the broken - at least if I understand that
correctly - file pci_epc.c is also authored by Xiaomi. Anyway, back to
the topic at hand.)
If my research above is correct, then in-tree code has only a single use
case for the change added by the commit but incurs program memory size
penalty for all users (with varying impact.) In such case, I think this
should be made optional. (This may be up for discussion though - the
memory reduction I achieved is 1400 bytes on AVR but only 400 bytes on
rv-virt. The question is if the code clutter - albeit a small one - is
worth it for one less significant architecture.)
I prepared a patch that eliminates this program memory size increase if
the heap parameter is not actually used by anything. It wraps member
value FAR struct mm_heap_s *heap in struct mm_heap_config_s with #ifndef
CONFIG_MM_DISABLE_INIT_HEAP_POINTER , a new configuration option which
defaults to DEFAULT_SMALL. The RPTUN driver is made to depends on
!MM_DISABLE_INIT_HEAP_POINTER . Other than that, mm_initialize_heap adds
multiple #ifndef directives to eliminate code related to heap parameter.
This approach has two benefits:
1. if more users of the heap parameter are added but not made to depend
on !MM_DISABLE_INIT_HEAP_POINTER, build with DEFAULT_SMALL will fail -
no hidden errors
2. other users of struct mm_heap_config_s use memset to clear it before
use. The heap parameter is not set so no code change is needed for those
calls
The patch is available in a git repository nuttx.git at git.kerogit.eu
accessible through HTTP/S. (Trying to prevent bot traffic by not posting
the URL in machine-readable form.) The relevant branch is called
mm_init_optional_heap. If someone has the time to look at it and provide
feedback and/or create pull request on GitHub (I don't have an account),
it would be greatly appreciated. I think the change is quite trivial to
be reasonably sure that it does not break anything but this is
definitively an area where I only have a vague understanding of the code
at best.
As of note - I did some tests of the change but there was one thing I
was not able to test - the RPTUN driver itself. Don't have any hardware
to try with and I wasn't even able to compile it for AVR (well, to be
more precise - when I tried, it started downloading things from the web
so I stopped the build.)
Following is for the GitHub PR (if it comes to it)
================
Summary
Make heap parameter of function mm_initialize_heap optional in
mm/mm_heap/mm_initialize.c
Problem:
Parameter heap added in commit 6ed4ea63d8168be30227415ea85ae936ca41bb6f
necessitates call of function mm_memalign which can otherwise be
eliminated from compiled binary on small architectures, namely 8-bit AVR
DA/DB family. This increases program memory consumption by 1400 bytes on
that architecture. This parameter is currently only used by RPTUN
driver.
Solution:
Add MM_DISABLE_INIT_HEAP_POINTER configuration option which removes this
parameter and the associated code, if set
Impact
Users: will be able to use more program memory for their application
code
Build:
- new Kconfig option MM_DISABLE_INIT_HEAP_POINTER, defaults to
DEFAULT_SMALL
- rptun driver depends on !MM_DISABLE_INIT_HEAP_POINTER
Compatibility:
- no functional change for architectures/boards that do not set
DEFAULT_SMALL
- architectures that set DEFAULT_SMALL will be unable to build rptun
driver unless the new option is unset manually
Testing
Test 1
Hardware: AVR128DA28 (NSH build for breadxavr board)
Tests performed:
- build test with the new option unset to verify that code does not
change
- build test with the new option set to verify that the code is
functional
Before the patch:
$ make
Register: nsh
Register: sh
LD: nuttx
Memory region Used Size Region Size %age Used
flash: 51489 B 128 KB 39.28%
sram: 636 B 16 KB 3.88%
eeprom: 0 B 512 B 0.00%
rodata: 592 B 4 KB 14.45%
CP: nuttx.hex
CP: nuttx.asm
$ sha256sum nuttx
818bad0a984a3b75ccd0f138e4bfcfa00264807b9a9d6d16683ea42eac01413d nuttx
After the patch (new option not set)
$ make
LD: nuttx
Memory region Used Size Region Size %age Used
flash: 51489 B 128 KB 39.28%
sram: 636 B 16 KB 3.88%
eeprom: 0 B 512 B 0.00%
rodata: 592 B 4 KB 14.45%
CP: nuttx.hex
CP: nuttx.asm
$ sha256sum nuttx
818bad0a984a3b75ccd0f138e4bfcfa00264807b9a9d6d16683ea42eac01413d nuttx
Result - the patch does not change the compiled binary when the new
configuration option is not enabled
After the patch (new option set)
$ make
LD: nuttx
Memory region Used Size Region Size %age Used
flash: 50079 B 128 KB 38.21%
sram: 636 B 16 KB 3.88%
eeprom: 0 B 512 B 0.00%
rodata: 592 B 4 KB 14.45%
CP: nuttx.hex
CP: nuttx.asm
$ minicom
Welcome to minicom 2.10
OPTIONS: I18n
Port /dev/serial/by-id/usb-FTDI_FT230X_Basic_UART_DU0DQ17J-if00-port0,
16:37:48 [U]
Press CTRL-A Z for help on special keys
NuttShell (NSH) NuttX-12.12.0
nsh> help
help usage: help [-v] [<cmd>]
? help
nsh>
Result - NSH is functional and flash usage is reduced
Test 2
Hardware: building for Risc-V Qemu - rv-virt:nsh
Tests performed:
- build test with the new option unset to verify that code does not
change, run in Qemu, run ostest
- build test with the new option set to verify that code runs correctly,
run in Qemu, run ostest
Before the patch
$ sha256sum nuttx nuttx.asm
9c68c09fae0effec154957ed0a3b45b9e45879d708c3cd55f15f7be3c07c443d nuttx
146c24fad25f74f923b7398fbce5310adfdb88fc3875ed5127f74c058ebf7c60
nuttx.asm
ostest:
dump_assert_info: Current Version: NuttX 12.12.0 b4242042e1 Feb 22 2026
14:44:13 risc-v
...
ostest_main: Exiting with status 0
After the patch (new option in default state, ie. unset)
$ sha256sum nuttx nuttx.asm
79005fc3be7f240896caa2b03b231254f903705b38bfc1eefeb263da880f7150 nuttx
146c24fad25f74f923b7398fbce5310adfdb88fc3875ed5127f74c058ebf7c60
nuttx.asm
dump_assert_info: Current Version: NuttX 12.12.0 ee396982d7 Feb 22 2026
15:46:21 risc-v
...
ostest_main: Exiting with status 0
Result - the resulting binary does differ but the disassembly does not.
Ostest completes successfully.
After the patch (new option set)
Program size reduced by cca 400 bytes (compared by last instruction's
address in disassembly.)
dump_assert_info: Current Version: NuttX 12.12.0 ee396982d7 Feb 22 2026
16:24:11 risc-v
...
ostest_main: Exiting with status 0
NOTE - RPTUN driver, the only user of the (optionally removed) heap
parameter, was not tested - no access to relevant hardware.
================
Thanks for your time
