Re: [PATCH] reserve_early end-of-conventional-memory to 1MB II - some numbers to put it into perspective

H. Peter Anvin
2008-02-27T16:45:28Z

Andi Kleen wrote:
>
> Just to give some perspective of this:
>
> On my laptop here
>
> BIOS-e820: 000000000009dc00 - 00000000000a0000 (reserved)
> BIOS-e820: 00000000000d2000 - 0000000000100000 (reserved)
>
> This means it reserves only ~193KB in the 640k-1MB area
>
> With this patch it will reserve 384KB instead. This means 191KB
> are lost. While that doesn't sound too much it worth as much as
> 382 patches that reduce kernel code size by 512bytes or
> worth 3820 patches that reduce kernel code by 100 bytes in terms
> of memory consumption.
>
> Now such kernel code size patches are always popular, but why undo that
> work by throwing away perfectly good memory elsewhere?
>
> Or also the laptop kernel does
>
> Freeing unused kernel memory: 340k freed
>
> This means the 193KB now lost are worth 56% of the complete
> memory that is freed by __initdata/__init. Just maintaining
> these annotations is a lot of work, but why do all that if we
> then throw away than half as much memory as they save so easily?
>

It doesn't waste any memory at all.

It arguably wastes some *address space*, but that's an entirely
different thing.

Unless you have chipset-specific drivers to enable memory in the
640-1024K memory area, there is nothing there.

-hpa