Re: Slow boot with 256GB of RAM?

On 16 November 2013 17:49, Eitan Adler <lists_at_eitanadler.com> wrote:
> On Sat, Nov 16, 2013 at 4:12 PM, Zach Crum <crum.zach_at_gmail.com> wrote:
>> This setting is not listed in /boot/defaults/loader.conf. Is it supposed to
>> be singular or plural?
>
> Plural.
>
> I will commit the patch.

The FAQ update patch looks fine.

> Does any know of cases where this memory test actually catches errors?
>  How important is it?

The boot time test is primarily of historical significance, and
doesn't really provide value on contemporary systems.  It's mainly a
workaround for ancient broken BIOSes that might return bogus memory
map data.  I intend to commit the patch below that disables it by
default.

The variable name is "hw.memtest.tests" as it's intended to be
extended to a bitmap of tests to run at boot, with other bits
representing more comprehensive tests.

-Ed

commit 58f501f70427ce2aeb9c8b18d2b7bec543818dae
Author: Ed Maste <emaste_at_freebsd.org>
Date:   Thu Nov 21 12:31:06 2013 -0500

    Disable amd64 boot time memory test by default

    The page presence memory test takes a long time on large memory systems
    and has little value on contemporary amd64 hardware.

diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
index 7f05d58..df03e55 100644
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
_at__at_ -1476,13 +1476,15 _at__at_ getmemsize(caddr_t kmdp, u_int64_t first)
                Maxmem = atop(physmem_tunable);

        /*
-        * By default enable the memory test on real hardware, and disable
-        * it if we appear to be running in a VM.  This avoids touching all
-        * pages unnecessarily, which doesn't matter on real hardware but is
-        * bad for shared VM hosts.  Use a general name so that
-        * one could eventually do more with the code than just disable it.
+        * The boot memory test is disabled by default, as it takes a
+        * significant amount of time on large-memory systems, and is
+        * unfriendly to virtual machines as it unnecessarily touches all
+        * pages.
+        *
+        * A general name is used as the code may be extended to support
+        * additional tests beyond the current "page present" test.
         */
-       memtest = (vm_guest > VM_GUEST_NO) ? 0 : 1;
+       memtest = 0;
        TUNABLE_ULONG_FETCH("hw.memtest.tests", &memtest);

        /*