Re: [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@xxxxxxxxxxx>
---
  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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