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SubjectRe: [PATCH] MIPS: Refactor early_parse_mem() to fix mem= parameter
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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.

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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