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Message-ID: <CAErSpo6UwL6kY4rHeYQbn1kghJH-kQDeat7VXp95JE2pGER5ZA@mail.gmail.com>
Date: Tue, 12 Jun 2012 04:30:33 -0700
From: Bjorn Helgaas <bhelgaas@...gle.com>
To: Wen Congyang <wency@...fujitsu.com>
Cc: rob@...dley.net, tglx@...utronix.de,
Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2 v2] x86: add max_addr boot option
On Mon, Jun 11, 2012 at 11:29 PM, Wen Congyang <wency@...fujitsu.com> wrote:
> At 06/12/2012 01:35 AM, Bjorn Helgaas Wrote:
>> On Mon, Jun 11, 2012 at 1:44 AM, Wen Congyang <wency@...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.
>
> Currently, I only need to ignore the memory. If we need to ignore a node,
> "numa_node=" or similar parameter is a better choice.
Doesn't the end user have to know the memory map of the system to use
"max_addr="? How do you know what value to supply? Do you have to
attempt a boot once to discover the highest address on node 0? What
if node 0 and node 1 memory are interleaved, so there's some node 1
memory below the highest node 0 address?
>>> Signed-off-by: Wen Congyang <wency@...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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>
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