On Nov 24, 2008, at 6:10 PM, Michael Ellerman wrote:

On Mon, 2008-11-24 at 14:07 -0600, Hollis Blanchard wrote:

quoted

On Fri, 2008-11-14 at 16:09 -0600, Hollis Blanchard wrote:

quoted

If this is all too much, then I'm close to giving up and burning a
64KB page, which requires only ALIGN_DOWN() in the kernel.

ppc: force memory size to be a multiple of PAGE_SIZE

Ensure that total memory size is page-aligned, because otherwise
bootmem.c gets upset.

This error case was triggered by using 64 KiB pages in the kernel 
while
arch/powerpc/boot/4xx.c arbitrarily reduced the amount of memory by 
4096 (to
work around the "CHIP11" errata which affects the last 256 bytes of 
physical memory).

Signed-off-by: Hollis Blanchard <redacted>
---
This is on a common code path, and lmb_enforce_memory_limit() will now
always take action, so wider testing would be good.

This patch supercedes http://patchwork.ozlabs.org/patch/8211/ .

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c

@@ -1200,6 +1200,11 @@ void __init early_init_devtree(void *par
 	early_reserve_mem();
 	phyp_dump_reserve_mem();

+	/* Ensure that total memory size is page-aligned, because otherwise
+	 * bootmem.c gets upset. */
+	lmb_analyze();
+	memory_limit = lmb_phys_mem_size() & PAGE_MASK;

All of the current code using memory_limit looks like it'll be safe 
with
this change, although there are several cases of this we could remove:

if (memory_limit && <some other condition>)

Because memory_limit will now always be true.

memory_limit was the result of parsing mem= from the command line.   
Does this break that?

Still, I think it would be better to only set memory_limit when the mem
size is not a multiple of the PAGE_SIZE - so that memory_limit retains
it's function as both the value of the limit and a boolean.

I would have expected this trimming to occur where we actually transfer 
the memory from lmb to bootmem, since it is bootmem that has the 
aligned size requirement.

milton