[Xen-devel] [PATCH] xen: allow extra memory stay within lowest available range

[Jacob Shin <jacob.shin@xxxxxxx>]

We have a machine with 1.5 TB of memory which has a e820 that looks 
like this:

(XEN)  0000000000000000 - 000000000008f400 (usable)
(XEN)  000000000008f400 - 00000000000a0000 (reserved)
(XEN)  00000000000d0000 - 0000000000100000 (reserved)
(XEN)  0000000000100000 - 00000000c7eb0000 (usable)
(XEN)  00000000c7eb0000 - 00000000c7ed8000 (ACPI data)
(XEN)  00000000c7ed8000 - 00000000c7eda000 (ACPI NVS)
(XEN)  00000000c7eda000 - 00000000c8000000 (reserved)
(XEN)  00000000c8000000 - 00000000c8001000 (reserved)
(XEN)  00000000d8000000 - 00000000d8001000 (reserved)
(XEN)  00000000d8400000 - 00000000d8401000 (reserved)
(XEN)  00000000d8800000 - 00000000d8801000 (reserved)
(XEN)  00000000fec00000 - 00000000fec10000 (reserved)
(XEN)  00000000fee00000 - 00000000fee01000 (reserved)
(XEN)  00000000fff00000 - 0000000100000000 (reserved)
(XEN)  0000000100000000 - 000000f038000000 (usable)
(XEN)  000000f038000000 - 000000fd00000000 (reserved)
(XEN)  0000010000000000 - 0000018fff000000 (usable)

Booting with dom0_mem=1024M, 2.6.32.48 adds extra pages for ballooning
at the end, and Dom0 panics:

..
[    0.000000]  Xen: 00000000fff00000 - 0000000100000000 (reserved)
[    0.000000]  Xen: 000000f038000000 - 000000fd00000000 (reserved)
[    0.000000]  Xen: 000000fd00000000 - 000000ff40000000 (usable)
..
[    0.000000] init_memory_mapping: 0000000100000000-000000ff40000000
[    0.000000]  0100000000 - ff40000000 page 4k
[    0.000000] Kernel panic - not syncing: Cannot find space for the kernel 
page tables
..
[    0.000000]  [<ffffffff816699f9>] panic+0x8c/0x1a2
[    0.000000]  [<ffffffff81642da6>] init_memory_mapping+0x3d4/0x4b9
[    0.000000]  [<ffffffff81d068ba>] setup_arch+0x651/0xaaa
[    0.000000]  [<ffffffff81669b4b>] ? printk+0x3c/0x3e
[    0.000000]  [<ffffffff8166ba03>] ? _raw_spin_unlock_irqrestore+0x10/0x12
[    0.000000]  [<ffffffff81d00aa7>] start_kernel+0x8f/0x3ca
[    0.000000]  [<ffffffff81d002cb>] x86_64_start_reservations+0xb6/0xba
[    0.000000]  [<ffffffff81d04002>] xen_start_kernel+0x5a0/0x5a7

Below patch allows extra memory to settle on the first available memory
range that can accommodate it. Resulting e820 looks like this:

[    0.000000]  Xen: 00000000fff00000 - 0000000100000000 (reserved)
[    0.000000]  Xen: 0000000100000000 - 0000000340000000 (usable)
[    0.000000]  Xen: 000000f038000000 - 000000fd00000000 (reserved)

This patch is moot on 3.2 and later because another patch already handles
this case: dc91c728fddc29dfed1ae96f6807216b5f42d3a1 xen: allow extra
memory to be in multiple regions.

Signed-off-by: Jacob Shin <jacob.shin@xxxxxxx>
---
 arch/x86/xen/setup.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 46d6d21..1ce626d 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -240,6 +240,7 @@ char * __init xen_memory_setup(void)
        memcpy(map_raw, map, sizeof(map));
        e820.nr_map = 0;
        xen_extra_mem_start = mem_end;
+       extra_limit = xen_get_max_pages();
        for (i = 0; i < memmap.nr_entries; i++) {
                unsigned long long end;
 
@@ -268,7 +269,9 @@ char * __init xen_memory_setup(void)
                }
 
                if (map[i].size > 0 && end > xen_extra_mem_start)
-                       xen_extra_mem_start = end;
+                       if (PFN_DOWN(map[i].addr - xen_extra_mem_start) <
+                               (extra_limit - max_pfn))
+                               xen_extra_mem_start = end;
 
                /* Add region if any remains */
                if (map[i].size > 0)
@@ -305,7 +308,6 @@ char * __init xen_memory_setup(void)
 
        sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
 
-       extra_limit = xen_get_max_pages();
        if (max_pfn + extra_pages > extra_limit) {
                if (extra_limit > max_pfn)
                        extra_pages = extra_limit - max_pfn;
-- 
1.7.8.4



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