Hi Dave,
On 10/24/17 at 01:31pm, Dave Young wrote:
> The total memory size we get in kernel is usually slightly less than 2G with a
> 2G memory module machine. The main reason is bios/firmware reserve some area
> it will not export all memory as usable to Linux.
>
> 2G memory X86 kvm guest test result of the total_mem value:
> UEFI boot with ovmf: 0x7ef10000
> Legacy boot kvm guest: 0x7ff7cc00
>
> An option is to use dmi/smbios to get physical memory size, but it's not
> reliable as well. According to Prarit hardware vendors sometimes screw this up.
> Thus we choose to round up total size to 128M to workaround this problem.
> This is a best effort workaround, will improve it when we have better way
> in the future.
Thanks for this posting. While I don't get the point of this patch. So
firmware take piece of memory, then why we need to count it into the
total memory which we want to calculate a crashkernel memory based on.
Not counting that, is there anyting incorrect?
Thanks
Baoquan
>
> Signed-off-by: Dave Young <dyoung at redhat.com>
> ---
> kernel/crash_core.c | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> --- linux.orig/kernel/crash_core.c
> +++ linux/kernel/crash_core.c
> @@ -42,6 +42,15 @@ static int __init parse_crashkernel_mem(
> {
> char *cur = cmdline, *tmp;
> bool infinite_end = false;
> + unsigned long long total_mem = system_ram;
> +
> + /*
> + * Firmware usually reserves some memory regions for it's own use.
> + * so we get less than actual system memory size.
> + * We workaround this by round up the total size to 128M which is
> + * enough for most test cases.
> + */
> + total_mem = roundup(total_mem, 0x8000000);
>
> /* for each entry of the comma-separated list */
> do {
> @@ -86,13 +95,13 @@ static int __init parse_crashkernel_mem(
> return -EINVAL;
> }
> cur = tmp;
> - if (size >= system_ram) {
> + if (size >= total_mem) {
> pr_warn("crashkernel: invalid size\n");
> return -EINVAL;
> }
>
> /* match ? */
> - if (system_ram >= start && system_ram < end) {
> + if (total_mem >= start && total_mem < end) {
> *crash_size = size;
> if (end == ULLONG_MAX)
> infinite_end = true;
> @@ -126,9 +135,9 @@ static int __init parse_crashkernel_mem(
> pr_warn("Memory reservation scale order expected after '^'\n");
> return -EINVAL;
> }
> - size = (system_ram - *crash_size) >> shift;
> + size = (total_mem - *crash_size) >> shift;
> size = *crash_size + roundup(size, 1ULL << 20);
> - if (size < system_ram)
> + if (size < total_mem)
> *crash_size = size;
> cur = tmp;
> } else
>
>
