Hi Baoquan,
On 10/24/17 at 01:57pm, Baoquan He wrote:
> 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?
Yes, considering crashkernel=1G-2G:128M, if we have a 1G memory
machine, we get total size 1023M from firmware then it will not fall
into 1G-2G thus no memory reserved. User will never know that, it is
hard to let user to know the exact total value we get in kernel..
>
> Thanks
> Baoquan
>
> >
> > Signed-off-by: Dave Young <dyo...@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
> >
> >
Thanks
Dave
