Re: How to detect the amount of RAM on non-EFI platforms?

[Cyan Yang]

Hi,

On 2023/7/14 22:04, Vladimir 'phcoder' Serbinenko wrote:
>
> Just add an option to consider "reserved" memory as available. User's
> choice. Fire you it's a single if.
>
Thanks for the tip, but I don't think it will work out - if we add up
the reserved section, the result will be more than actual amount. I ran
a test to show this.

Consider a VM with EFI firmware (x86_64-efi) with 16,384MiB of RAM, I
built and ran the module with memory map info printed out. Here's the
result (output is way too long):

grub> phymem
Memory map 0001 @ 0x0000000000000000, with size of 0x87000
Memory map 0001 @ 0x0000000000087000, with size of 0x1000
Memory map 0001 @ 0x0000000000088000, with size of 0x18000
Memory map 0001 @ 0x0000000000100000, with size of 0x706000
Memory map 0001 @ 0x0000000000806000, with size of 0x1000
Memory map 0001 @ 0x0000000000807000, with size of 0x4000
Memory map 0001 @ 0x000000000080b000, with size of 0x1000
Memory map 0001 @ 0x000000000080c000, with size of 0x14000
Memory map 0001 @ 0x0000000000820000, with size of 0xce0000
Memory map 0001 @ 0x0000000001500000, with size of 0x5b548000
Memory map 0001 @ 0x000000005ca48000, with size of 0x1f576000
Memory map 0001 @ 0x000000007bfbe000, with size of 0x20000
Memory map 0001 @ 0x000000007bfde000, with size of 0x22f3000
Memory map 0001 @ 0x000000007e2d1000, with size of 0x25000
Memory map 0001 @ 0x000000007e2f6000, with size of 0x26000
Memory map 0001 @ 0x000000007e31c000, with size of 0x10000
Memory map 0001 @ 0x000000007e32c000, with size of 0x1000
Memory map 0001 @ 0x000000007e32d000, with size of 0x1000
Memory map 0001 @ 0x000000007e32e000, with size of 0x79e000
Memory map 0001 @ 0x000000007eacc000, with size of 0xa7000
Memory map 0001 @ 0x000000007eb73000, with size of 0x26000
Memory map 0001 @ 0x000000007eb99000, with size of 0x9e000
Memory map 0001 @ 0x000000007ec37000, with size of 0x3c000
Memory map 0001 @ 0x000000007ec73000, with size of 0x5000
Memory map 0001 @ 0x000000007ec78000, with size of 0x1000
Memory map 0001 @ 0x000000007ec79000, with size of 0x20000
Memory map 0001 @ 0x000000007ec99000, with size of 0x1000
Memory map 0001 @ 0x000000007ec9a000, with size of 0x7000
Memory map 0001 @ 0x000000007eca1000, with size of 0x2000
Memory map 0001 @ 0x000000007eca3000, with size of 0xa000
Memory map 0001 @ 0x000000007ecad000, with size of 0x1000
Memory map 0001 @ 0x000000007ecae000, with size of 0x11000
Memory map 0001 @ 0x000000007ecbf000, with size of 0x2000
Memory map 0001 @ 0x000000007ecc1000, with size of 0x4000
Memory map 0001 @ 0x000000007ecc5000, with size of 0x4000
Memory map 0001 @ 0x000000007ecc9000, with size of 0x1a000
Memory map 0001 @ 0x000000007ece3000, with size of 0x5000
Memory map 0001 @ 0x000000007ece8000, with size of 0x14000
Memory map 0001 @ 0x000000007ecfc000, with size of 0xb000
Memory map 0001 @ 0x000000007ed07000, with size of 0x15000
Memory map 0001 @ 0x000000007ed1c000, with size of 0x1000
Memory map 0001 @ 0x000000007ed1d000, with size of 0x7000
Memory map 0001 @ 0x000000007ed24000, with size of 0x7000
Memory map 0001 @ 0x000000007ed2b000, with size of 0x1c000
Memory map 0001 @ 0x000000007ed47000, with size of 0x2000
Memory map 0001 @ 0x000000007ed49000, with size of 0x14000
Memory map 0001 @ 0x000000007ed5d000, with size of 0x7000
Memory map 0001 @ 0x000000007ed64000, with size of 0x6000
Memory map 0001 @ 0x000000007ed6a000, with size of 0x1000
Memory map 0001 @ 0x000000007ed6b000, with size of 0x1d000
Memory map 0001 @ 0x000000007ed88000, with size of 0x3000
Memory map 0001 @ 0x000000007ed8b000, with size of 0xe000
Memory map 0001 @ 0x000000007ed99000, with size of 0x2000
Memory map 0001 @ 0x000000007ed9b000, with size of 0x14000
Memory map 0001 @ 0x000000007edaf000, with size of 0x2000
Memory map 0001 @ 0x000000007edb1000, with size of 0xd000
Memory map 0001 @ 0x000000007edbe000, with size of 0x3000
Memory map 0001 @ 0x000000007edc1000, with size of 0x6000
Memory map 0001 @ 0x000000007edc7000, with size of 0x2000
Memory map 0001 @ 0x000000007edc9000, with size of 0x1000
Memory map 0001 @ 0x000000007edca000, with size of 0x1000
Memory map 0001 @ 0x000000007edcb000, with size of 0x5000
Memory map 0001 @ 0x000000007edd0000, with size of 0x5000
Memory map 0001 @ 0x000000007edd5000, with size of 0x12000
Memory map 0001 @ 0x000000007ede7000, with size of 0x2000
Memory map 0001 @ 0x000000007ede9000, with size of 0x6000
Memory map 0001 @ 0x000000007edef000, with size of 0x2000
Memory map 0001 @ 0x000000007edf1000, with size of 0xf000
Memory map 0001 @ 0x000000007ee00000, with size of 0x200000
Memory map 0001 @ 0x000000007f000000, with size of 0xc000
Memory map 0001 @ 0x000000007f00c000, with size of 0x5000
Memory map 0001 @ 0x000000007f011000, with size of 0x12000
Memory map 0001 @ 0x000000007f023000, with size of 0x2000
Memory map 0001 @ 0x000000007f025000, with size of 0x1000
Memory map 0001 @ 0x000000007f026000, with size of 0x1000
Memory map 0001 @ 0x000000007f027000, with size of 0x7000
Memory map 0001 @ 0x000000007f02e000, with size of 0x7000
Memory map 0001 @ 0x000000007f035000, with size of 0x4000
Memory map 0001 @ 0x000000007f039000, with size of 0x6000
Memory map 0001 @ 0x000000007f03f000, with size of 0x4000
Memory map 0001 @ 0x000000007f043000, with size of 0x2000
Memory map 0001 @ 0x000000007f045000, with size of 0x2b000
Memory map 0001 @ 0x000000007f070000, with size of 0xa000
Memory map 0001 @ 0x000000007f07a000, with size of 0xa000
Memory map 0001 @ 0x000000007f084000, with size of 0x4000
Memory map 0002 @ 0x000000007f088000, with size of 0xc1000
Memory map 0001 @ 0x000000007f149000, with size of 0x15000
Memory map 0001 @ 0x000000007f15e000, with size of 0x3000
Memory map 0001 @ 0x000000007f161000, with size of 0x3000
Memory map 0001 @ 0x000000007f164000, with size of 0x2000
Memory map 0001 @ 0x000000007f166000, with size of 0x5000
Memory map 0001 @ 0x000000007f16b000, with size of 0x1000
Memory map 0001 @ 0x000000007f16c000, with size of 0x1000
Memory map 0001 @ 0x000000007f16d000, with size of 0x1000
Memory map 0001 @ 0x000000007f16e000, with size of 0x1000
Memory map 0001 @ 0x000000007f16f000, with size of 0x1000
Memory map 0001 @ 0x000000007f170000, with size of 0x1000
Memory map 0001 @ 0x000000007f171000, with size of 0x2000
Memory map 0001 @ 0x000000007f173000, with size of 0x3000
Memory map 0001 @ 0x000000007f176000, with size of 0x2000
Memory map 0001 @ 0x000000007f178000, with size of 0x1000
Memory map 0001 @ 0x000000007f179000, with size of 0x42000
Memory map 0001 @ 0x000000007f1bb000, with size of 0xc000
Memory map 0001 @ 0x000000007f1c7000, with size of 0x1000
Memory map 0001 @ 0x000000007f1c8000, with size of 0x1000
Memory map 0001 @ 0x000000007f1c9000, with size of 0x1000
Memory map 0001 @ 0x000000007f1ca000, with size of 0x1000
Memory map 0001 @ 0x000000007f1cb000, with size of 0x2000
Memory map 0001 @ 0x000000007f1cd000, with size of 0x6000
Memory map 0001 @ 0x000000007f1d3000, with size of 0x400000
Memory map 0001 @ 0x000000007f5d3000, with size of 0x4000
Memory map 0001 @ 0x000000007f5d7000, with size of 0x1000
Memory map 0001 @ 0x000000007f5d8000, with size of 0x2000
Memory map 0001 @ 0x000000007f5da000, with size of 0x2000
Memory map 0001 @ 0x000000007f5dc000, with size of 0x1000
Memory map 0001 @ 0x000000007f5dd000, with size of 0x1000
Memory map 0001 @ 0x000000007f5de000, with size of 0x9000
Memory map 0001 @ 0x000000007f5e7000, with size of 0x3000
Memory map 0001 @ 0x000000007f5ea000, with size of 0x3000
Memory map 0001 @ 0x000000007f5ed000, with size of 0x302000
Memory map 0002 @ 0x000000007f8ef000, with size of 0x100000
Memory map 0014 @ 0x000000007f9ef000, with size of 0x100000
Memory map 0002 @ 0x000000007faef000, with size of 0x80000
Memory map 0003 @ 0x000000007fb6f000, with size of 0x10000
Memory map 0004 @ 0x000000007fb7f000, with size of 0x80000
Memory map 0001 @ 0x000000007fbff000, with size of 0x201000
Memory map 0001 @ 0x000000007fe00000, with size of 0xe9000
Memory map 0001 @ 0x000000007fee9000, with size of 0x20000
Memory map 0001 @ 0x000000007ff09000, with size of 0x1a000
Memory map 0001 @ 0x000000007ff23000, with size of 0x42000
Memory map 0001 @ 0x000000007ff65000, with size of 0x17000
Memory map 0002 @ 0x000000007ff7c000, with size of 0x84000
Memory map 0001 @ 0x0000000100000000, with size of 0x380000000
Memory map 0002 @ 0x00000000b0000000, with size of 0x10000000
Memory map 0002 @ 0x00000000ffc00000, with size of 0x400000
The total system memory is 16643 MiB (17452105728 Bytes).

As you can see, the reported amount will be more than actual amount.
This is even twice the amount if a machine has only a hundred of RAM.

BTW, I am considering to move the thread to discuss the way to precisely
detect the amount of system memory, as the original issue was resolved.

Thanks,
Cinhi Young