Memory usage analysis and optimization

[Jesse-SC Chou (周書正)]

Hi L4-hackers,

I’m analyzing the memory usage of Fiasco/L4Re/L4Linux.
On my platform, there are 128MB physical memory.
L4 bootstrap can detect it correctly.
==================================================
L4 Bootstrapper
  Build: #164 拻 12堎  9 11:39:51 CST 2016, 4.8.4
  Scanning up to 128 MB RAM, starting at offset 32MB
  Memory size is 128MB (20000000 - 27ffffff)
  RAM: 0000000020000000 - 0000000027ffffff: 131072kB
  Total RAM: 128MB
==================================================

The memory regions after boot up and sigma0 loaded:
==================================================
Regions of list 'regions'
    [ 20000000,  200001c7] {      1c8} Root   mbi_rt
    [ 20001000,  20001aff] {      b00} Kern   fiasco
    [ 20002000,  20092fff] {    91000} Kern   fiasco
    [ 200c0000,  200c9f43] {     9f44} Sigma0 sigma0
    [ 200d0000,  200d6177] {     6178} Sigma0 sigma0
    [ 20140000,  20168c27] {    28c28} Root   moe
    [ 20170000,  2017b58b] {     b58c} Root   moe
    [ 21000000,  2100e5e3] {     e5e4} Boot   bootstrap
    [ 21100000,  21a2dfff] {   92e000} Root   Module

SIGMA0: Hello!
  KIP @ 20002000
  allocated 4KB for maintenance structures
SIGMA0: Dump of all resource maps
RAM:------------------------
[4:20000000;20000fff]
[0:20093000;200bffff]
[0:200ca000;200cffff]
[0:200d7000;2013ffff]
[4:20140000;20168fff]
[0:20169000;2016ffff]
[4:20170000;2017bfff]
[0:2017c000;210fffff]
[4:21100000;21a2dfff]
[0:21a2e000;26ffffff]
==================================================

The largest unused continuous memory region are at “0x21a2e000 ~ 0x26ffffff”, which is about 85MB.
I would like to make continuous memory region larger and have the following ideas and questions:


1.      The memory used by bootstrap may be freed after the system bring up. If moving “bootstrap” program to 0x26000000, the “Module” programs can append to “MOE” program. The “Module” will be started “0x207c0000” (aligned to page size 4KB). Thus, I can get larger continuous memory area that originally separated by “bootstrap” program. Is this idea correct ?

    [ 20170000,  2017b58b] {     b58c} Root   moe
    [ 21000000,  2100e5e3] {     e5e4} Boot   bootstrap
    [ 21100000,  21a2dfff] {   92e000} Root   Module


2.      There are a reserved region “0x27000000 ~ 0x27FFFFFF” not shown in boot log. When I traced into program, this region seems used by sigma0. What is this memory used for? I think 16MB is a very large chunk in current embedded system. Can we compute the amount this area really use and shrink to a smaller size?

Any suggestion is very appreciated. Thanks.

BRs,
Jesse
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