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    SubjectRe: [PATCH 1/2 v2] x86: add max_addr boot option
    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
    >
    --
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