temp. mem mappings

DISCUSSION cohutta 3 participants 4 messages Jun 8, 2001 Memory management

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cohutta

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2001-06-08 01:38 UTC #0 lore raw

Quoted 10 lines

===== Original Message From "Stephen C. Tweedie" <[email protected]> ===== Hi,
Quoted 4 lines · cohutta
I think this is part of the problem: on my 1 GB system, the ACPI tables are at physical 0x3fffxxxx == virtual 0xffffxxxx, which could conflict with the APIC and IOAPIC mappings (from fixmap.h).

Quoted 4 lines

Shouldn't be --- the fixmaps should be part of the kernel's dynamic virtual area, which is not identity mapped. You can still map those physical addresses via kmap() on a highmem system (and a 1GB machine should be running a highmem kernel).

Well i now have a 768 MB machine, but i don't think that makes a big difference with the problem that i am seeing in mapping this ACPI memory early in setup_arch() [x86].

Quoted 7 lines

Quoted 2 lines
Well, i'm talking about physical memory, but it's marked as ACPI data.
If it is marked PG_Reserved, then ioremap() will work on it despite it being inside the normal physical memory area. If not, kmap() will still work.

Quoted 8 lines

Quoted 5 lines
Another part of the problem is that I need to do this early in arch/i386/kernel/setup.c::setup_arch(), like between calls to paging_init() and init_apic_mappings(). I can't use ioremap() here can i? ioremap() calls get_vm_area() which calls kmalloc(), and i don't think i can use kmalloc() just yet.
Right --- you can use alloc_pages but we haven't done the initialisation of the kmalloc slabsl by this point.

My testing indicates that i can't use __get_free_page(GFP_KERNEL) any time during setup_arch() [still x86]. It causes a BUG in slab.c (line 920) [linux 2.4.5]. Did I misunderstand you? Do you have another suggestion?

[for others who need it, not Stephen:
__get_free_page() -> __get_free_pages() -> alloc_pages() -> __alloc_pages() ]

Quoted 1 line

_Why_ do you need access to the ACPI tables so early, though?

ACPI tables have much to say about booting on newer x86 systems. I'll try to be more specific later, when i can.

Quoted 2 lines

Cheers,
Stephen

Thanks Stephen.
/c/

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Joseph A. Knapka

2001-06-08 17:02 UTC #1 lore raw

Quoted 33 lines · cohutta

Quoted 11 lines
===== Original Message From "Stephen C. Tweedie" <[email protected]> ===== Hi,
Quoted 4 lines · cohutta
I think this is part of the problem: on my 1 GB system, the ACPI tables are at physical 0x3fffxxxx == virtual 0xffffxxxx, which could conflict with the APIC and IOAPIC mappings (from fixmap.h).
Quoted 4 lines
Shouldn't be --- the fixmaps should be part of the kernel's dynamic virtual area, which is not identity mapped. You can still map those physical addresses via kmap() on a highmem system (and a 1GB machine should be running a highmem kernel).
Well i now have a 768 MB machine, but i don't think that makes a big difference with the problem that i am seeing in mapping this ACPI memory early in setup_arch() [x86].
Quoted 13 lines
Quoted 2 lines
Well, i'm talking about physical memory, but it's marked as ACPI data.
If it is marked PG_Reserved, then ioremap() will work on it despite it being inside the normal physical memory area. If not, kmap() will still work.
Quoted 5 lines
Another part of the problem is that I need to do this early in arch/i386/kernel/setup.c::setup_arch(), like between calls to paging_init() and init_apic_mappings(). I can't use ioremap() here can i? ioremap() calls get_vm_area() which calls kmalloc(), and i don't think i can use kmalloc() just yet.

Quoted 7 lines

Quoted 2 lines
Right --- you can use alloc_pages but we haven't done the initialisation of the kmalloc slabsl by this point.
My testing indicates that i can't use __get_free_page(GFP_KERNEL) any time during setup_arch() [still x86]. It causes a BUG in slab.c (line 920) [linux 2.4.5]. Did I misunderstand you? Do you have another suggestion?

Oops. You can't use __get_free_page() or alloc_pages() until mem_init() is called, which occurs in main/init.c:start_kernel() quite some time after setup_arch() has happened.

If you need pages before mem_init() happens, but after paging_init() has completed in setup_arch(), then use alloc_bootmem()/free_bootmem(). Any bootmem you alloc and don't free will end up being reserved.

-- Joe

-- Joseph A. Knapka
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Stephen C. Tweedie

2001-06-08 18:07 UTC #2 lore raw

In reply to cohutta

Hi,

Quoted 6 lines · cohutta

Quoted 2 lines
Right --- you can use alloc_pages but we haven't done the initialisation of the kmalloc slabsl by this point.
My testing indicates that i can't use __get_free_page(GFP_KERNEL) any time during setup_arch() [still x86]. It causes a BUG in slab.c (line 920) [linux 2.4.5].

After paging_init(), it should be OK --- as long as there is enough memory that you don't end up calling the VM try_to_free_page routines. Those will definitely choke this early in boot.

Cheers,
Stephen
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Joseph A. Knapka

2001-06-08 21:22 UTC #3 lore raw

Quoted 8 lines · Stephen C. Tweedie

Hi,
Quoted 3 lines · cohutta
Quoted 2 lines
Right --- you can use alloc_pages but we haven't done the initialisation of the kmalloc slabsl by this point.

Quoted 7 lines

Quoted 3 lines
My testing indicates that i can't use __get_free_page(GFP_KERNEL) any time during setup_arch() [still x86]. It causes a BUG in slab.c (line 920) [linux 2.4.5].
After paging_init(), it should be OK --- as long as there is enough memory that you don't end up calling the VM try_to_free_page routines. Those will definitely choke this early in boot.

But we don't actually give the zone allocator any free pages until mem_init().

- Joe