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Date: Thu, 04 Apr 2013 19:16:32 +0300
From: Andriy Gapon <avg@FreeBSD.org>
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To: John Baldwin <jhb@FreeBSD.org>
Subject: Re: gptzfsboot problem on HP P410i Smart Array
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Cc: Bjorn Larsson <bjwela@gmail.com>, freebsd-current@FreeBSD.org,
 Sergey Dyatko <sergey.dyatko@gmail.com>
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on 19/03/2013 18:20 John Baldwin said the following:
> Yes, we likely could start using that, we would just need to ensure it has some
> sort of minimum size.  However, maybe it would always have that minimum size as you
> are only going to have additional ranges if you have more than 4GB of RAM anyway.
> I think though that there were some odd BIOSes that would place a hole at 15-16MB,
> and for those the memory region at 1MB is too small.  A minimum size of 16MB might
> handle that case correctly while using the first extended region in the common
> case.

How about something like this?

Author: Andriy Gapon <avg@icyb.net.ua>
Date:   Wed Apr 3 11:48:34 2013 +0300

    [test] zfsboot: bios_getmem prefer extmem over another random chunk of high memory

    If the extended memory region is sufficiently large.

diff --git a/sys/boot/i386/zfsboot/zfsboot.c b/sys/boot/i386/zfsboot/zfsboot.c
index 82402b6..12ceeb0 100644
--- a/sys/boot/i386/zfsboot/zfsboot.c
+++ b/sys/boot/i386/zfsboot/zfsboot.c
@@ -374,6 +374,16 @@ bios_getmem(void)
     }

     /*
+     * If extended memory is at least twice as large as the largest
+     * region of higher memory, then carve the high heap out of
+     * extended memory.
+     */
+    if (bios_extmem > 2 * high_heap_size) {
+	high_heap_base = 0x100000 + bios_extmem / 2;
+	high_heap_size = bios_extmem / 2;
+    }
+
+    /*
      * If we have extended memory and did not find a suitable heap
      * region in the SMAP, use the last 3MB of 'extended' memory as a
      * high heap candidate.


-- 
Andriy Gapon