Boot time: Initial main memory initialization optimizations?

Hi,

regarding boot time optimization, on an embedded ARM Cortex-A9 based system with 512MB or 1GB main memory, we found that initializing this main memory takes a somehow large amount of time.

Initializing 512MB takes <= ~100ms, the additional 512MB on the 1GB take <= ~100ms additionally, too. So in sum <= ~200ms for 1GB.

Having a short look to this, it looks like most of the time is spent in arch/arm/mm/init.c in bootmem_init()/arm_bootmem_init()/arm_bootmem_free().

Has anybody already looked into this if there are any optimizations possible? Maybe even some hacks, if the main memory size (512MB/1GB) is always known? Any pointers?

I'm looking for reducing (a) the overall init time and maybe (b) the dependency on the memory size.

Thanks

Dirk

There were a couple of longish threads last year. Random links into the middle of 'em:

http://www.spinics.net/lists/linux-mm/msg54027.html
http://lkml.iu.edu//hypermail/linux/kernel/1306.3/01915.html

Basically they were deferring init by abusing the hotplug mechanism, so the system started with less memory and a background thread added more of it.

Rob