Memory usage analysis and optimization

[Adam Lackorzynski]

Hi,

On Fri Dec 16, 2016 at 08:38:28 +0000, Jesse-SC Chou (©P®Ñ¥¿) wrote:
> 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 Îå 12ÔÂ  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:

Generally: yes, there are tuning possibilities, given that memory and
program sizes are known.

> 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

Yes, should generally work I think.

> 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?

That's the memory taken by Fiasco, see src/kern/arm/config-arm.cpp
KMEMSIZE. Depending on your use case you can make this smaller.


Adam