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SubjectRe: [PATCH] MIPS: Refactor early_parse_mem() to fix mem= parameter
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On 02/25/2022 09:12 AM, Youling Tang wrote:
> Hi, Tiezhu
>
> On 02/24/2022 08:52 PM, Tiezhu Yang wrote:
>> According to Documentation/admin-guide/kernel-parameters.txt,
>> the kernel command-line parameter mem= means "Force usage of
>> a specific amount of memory", but when add "mem=3G" to the
>> command-line, kernel boot hangs in sparse_init().
>>
>> This commit is similar with the implementation of the other
>> archs such as arm64, powerpc and riscv, refactor the function
>> early_parse_mem() and then use memblock_enforce_memory_limit()
>> to limit the memory size.
>>
>> With this patch, when add "mem=3G" to the command-line, the
>> kernel boots successfully, we can see the following messages:
>>
>> [ 0.000000] Memory limited to 3072MB
>> ...
>> [ 0.000000] Memory: 2991952K/3145728K available (...)
>>
>> After login, the output of free command is consistent with the
>> above log.
>>
>> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
>> ---
>> arch/mips/kernel/setup.c | 25 ++++++++-----------------
>> 1 file changed, 8 insertions(+), 17 deletions(-)
>>
>> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
>> index f979adf..2917412 100644
>> --- a/arch/mips/kernel/setup.c
>> +++ b/arch/mips/kernel/setup.c
>> @@ -339,27 +339,15 @@ static void __init bootmem_init(void)
>> #endif /* CONFIG_SGI_IP27 */
>> static int usermem __initdata;
>> +static phys_addr_t memory_limit;
>> static int __init early_parse_mem(char *p)
>> {
>> - phys_addr_t start, size;
>> -
>> - /*
>> - * If a user specifies memory size, we
>> - * blow away any automatically generated
>> - * size.
>> - */
>> - if (usermem == 0) {
>> - usermem = 1;
>> - memblock_remove(memblock_start_of_DRAM(),
>> - memblock_end_of_DRAM() - memblock_start_of_DRAM());
>> - }
>> - start = 0;
>> - size = memparse(p, &p);
>> - if (*p == '@')
>> - start = memparse(p + 1, &p);
>> + if (!p)
>> + return 1;
>> - memblock_add(start, size);
>> + memory_limit = memparse(p, &p) & PAGE_MASK;
>> + pr_notice("Memory limited to %lldMB\n", memory_limit >> 20);
>> return 0;
>
> After applying this patch, my guess is that the kdump operation will fail.
>
> In the MIPS architecture, when the kdump operation is performed, a
> "mem=YM@XM" parameter will be added to the capture kernel (added by
> kexec-tools), indicating that the available memory range of the
> capture kernel is [X, X+Y).
>
> After the "mem" parameter is changed to the above, there will be only
> a similar parsing function like "mem=3G", and the type like
> "mem=128M@64M" cannot be correctly parsed.

Hi Youling,

Don't worry, it is another issue, I will take that into account
once this patch is applied.

This commit is the first step to fix the issue about mem=limit,
I think it is possible to support mem=limit@base and I will do
that later.

Thanks,
Tiezhu

>
> Thanks,
> Youling.
>> }
>> @@ -633,6 +621,9 @@ static void __init arch_mem_init(char **cmdline_p)
>> parse_early_param();
>> + /* Limit the memory size via mem= command-line parameter */
>> + memblock_enforce_memory_limit(memory_limit);
>> +
>> if (usermem)
>> pr_info("User-defined physical RAM map overwrite\n");
>>

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