Re: [PATCH 1/2 v2] x86: add max_addr boot option

Bjorn Helgaas
2012-06-11T17:35:37Z

On Mon, Jun 11, 2012 at 1:44 AM, Wen Congyang <wency@cn.fujitsu.com> wrote:
> Currently, the boot option max_addr is only supported on ia64 platform.
> We also need it on x86 platform.
> For example:
> There are two nodes:
>  NODE#0  address range 0x00000000 00000000 - 0x00010000 00000000
>  NODE#1  address range 0x00010000 00000000 - 0x00020000 00000000
> If we only want to use node0, we can specify the max_addr. The boot
> option "mem=" can do the same thing now. But the boot option "mem="
> means the total memory used by the system. If we tell the user
> that the boot option "mem=" can do this, it will confuse the user.
> So we need an new boot option "max_addr" on x86 platform.

I don't object to this patch (and thanks for tweaking the mem range printk).

I don't know what your use case is, but from a user interface
perspective, the "max_addr=" option feels like a bit of a hack. If
you're trying to avoid use of other nodes, "max_addr" is an awkward
way to do it. It requires the user to know the physical address ->
node mappings, and it doesn't affect the CPUs and I/O resources on
other nodes. You could implement a "numa_node=" or similar parameter
that would allow you to ignore remote memory, CPUs, and I/O.

> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
> ---
>  Documentation/kernel-parameters.txt |    2 +-
>  arch/x86/kernel/e820.c              |   36 +++++++++++++++++++++++++++++++++++
>  2 files changed, 37 insertions(+), 1 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index a92c5eb..034609d 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -1441,7 +1441,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>                         yeeloong laptop.
>                        Example: machtype=lemote-yeeloong-2f-7inch
>
> -       max_addr=nn[KMG]        [KNL,BOOT,ia64] All physical memory greater
> +       max_addr=nn[KMG]        [KNL,BOOT,ia64,X86] All physical memory greater
>                        than or equal to this physical address is ignored.
>
>        maxcpus=        [SMP] Maximum number of processors that an SMP kernel
> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> index 4185797..cd07226 100644
> --- a/arch/x86/kernel/e820.c
> +++ b/arch/x86/kernel/e820.c
> @@ -47,6 +47,7 @@ unsigned long pci_mem_start = 0xaeedbabe;
>  #ifdef CONFIG_PCI
>  EXPORT_SYMBOL(pci_mem_start);
>  #endif
> +static u64 max_addr = ~0ULL;
>
>  /*
>  * This function checks if any part of the range <start,end> is mapped
> @@ -119,6 +120,20 @@ static void __init __e820_add_region(struct e820map *e820x, u64 start, u64 size,
>                return;
>        }
>
> +       if (start >= max_addr) {
> +               printk(KERN_ERR "e820: ignoring [mem %#010llx-%#010llx]\n",
> +                      (unsigned long long)start,
> +                      (unsigned long long)(start + size - 1));
> +               return;
> +       }
> +
> +       if (max_addr - start < size) {
> +               printk(KERN_ERR "e820: ignoring [mem %#010llx-%#010llx]\n",
> +                      (unsigned long long)max_addr,
> +                      (unsigned long long)(start + size - 1));
> +               size = max_addr - start;
> +       }
> +
>        e820x->map[x].addr = start;
>        e820x->map[x].size = size;
>        e820x->map[x].type = type;
> @@ -835,6 +850,22 @@ static int __init parse_memopt(char *p)
>  }
>  early_param("mem", parse_memopt);
>
> +static int __init parse_memmax_opt(char *p)
> +{
> +       char *oldp;
> +
> +       if (!p)
> +               return -EINVAL;
> +
> +       oldp = p;
> +       max_addr = memparse(p, &p);
> +       if (p == oldp)
> +               return -EINVAL;
> +
> +       return 0;
> +}
> +early_param("max_addr", parse_memmax_opt);
> +
>  static int __init parse_memmap_opt(char *p)
>  {
>        char *oldp;
> @@ -881,6 +912,11 @@ early_param("memmap", parse_memmap_opt);
>
>  void __init finish_e820_parsing(void)
>  {
> +       if (max_addr != ~0ULL) {
> +               userdef = 1;
> +               e820_remove_range(max_addr, ULLONG_MAX - max_addr, E820_RAM, 1);
> +       }
> +
>        if (userdef) {
>                u32 nr = e820.nr_map;
>
> --
> 1.7.1
>