arch/ia64/kernel/efi.c

In doing some testing, I discovered the the mem= kernel command line option doesn't behave as expected for zx1 based machines. The current implementation assumes that memory starts at physical address zero and is physically contiguous, i.e. the mem= value is used as a limit on the physical address, rather than specifying the maximum physical memory to use.

I've enclosed a patch to fix the problem. Since this is primarily a debugging option, this isn't a critical fix.

John Marvin
[email protected]

@@ -210,6 +210,7 @@ efi_memmap_walk (efi_freemem_callback_t 
 	void *efi_map_start, *efi_map_end, *p, *q;
 	efi_memory_desc_t *md, *check_md;
 	u64 efi_desc_size, start, end, granule_addr, first_non_wb_addr = 0;
+       unsigned long mem_found = 0;
 
 	efi_map_start = __va(ia64_boot_param->efi_memmap);
 	efi_map_end   = efi_map_start + ia64_boot_param->efi_memmap_size;

@@ -259,14 +260,16 @@ efi_memmap_walk (efi_freemem_callback_t 
 		trim_top(md, first_non_wb_addr);
 
 		if (is_available_memory(md)) {
-			if (md->phys_addr + (md->num_pages << EFI_PAGE_SHIFT) > mem_limit) {
-				if (md->phys_addr > mem_limit)
+			if (mem_found + (md->num_pages << EFI_PAGE_SHIFT) > mem_limit) {
+				if (mem_found >= mem_limit)
 					continue;
-				md->num_pages = (mem_limit - md->phys_addr) >> EFI_PAGE_SHIFT;
+				md->num_pages = (mem_limit - mem_found) >> EFI_PAGE_SHIFT;
 			}
 
 			if (md->num_pages = 0)
 				continue;
+
+			mem_found += (md->num_pages << EFI_PAGE_SHIFT);
 
 			curr.start = PAGE_OFFSET + md->phys_addr;
 			curr.end   = curr.start + (md->num_pages << EFI_PAGE_SHIFT);

John Marvin <[email protected]> writes:

|> In doing some testing, I discovered the the mem= kernel command line option
|> doesn't behave as expected for zx1 based machines. The current implementation
|> assumes that memory starts at physical address zero and is physically
|> contiguous, i.e. the mem= value is used as a limit on the physical address,
|> rather than specifying the maximum physical memory to use.

IMHO the current behaviour is still useful. For example to make sure you have only memory below 4G you can say "mem=4G".

Andreas.

Andreas Schwab, SuSE Labs, [email protected]
SuSE Linux AG, Deutschherrnstr. 15-19, D-90429 Nürnberg
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

maybe it's useful, but it's not what the option is specified to do:

mem=nn[KMG] [KNL,BOOT] force use of a specific amount of
memory; to be used when the kernel is not able to see the whole system memory or for test.

Revolutions do not require corporate support.

Matthew> On Fri, Jul 26, 2002 at 03:50:03PM +0200, Andreas Schwab

Matthew> maybe it's useful, but it's not what the option is Matthew> specified to do:

Matthew> mem=nn[KMG] [KNL,BOOT] force use of a specific
Matthew> amount of memory; to be used when the kernel is not able to Matthew> see the whole system memory or for test.

I definitely want the old behavior. But we can rename the old behavior to "memlimit" or something like that. I'd be happy to apply such a patch.

	--david

Performance folks use this to characterize system performance too. They don't like to muck with HW any more than they have to.

We've used it in the past to work around platform issues - not just to "debug" them. It becomes critical if we discover we need such a workaround.

grant