[Xen-devel] What is the effect of EXTRA_MEM_RATIO

[Rushikesh Jadhav <2rushikeshj@xxxxxxxxx>]

Hi guys,

Im fairly new to the Xen Development & trying to understand ballooning.

While compiling a DomU kernel I'm trying to understand the e820 memory map w.r.t Xen,

I have modified arch/x86/xen/setup.c  EXTRA_MEM_RATIO  to 1 and can see that the guest can not balloon up more than 2GB. Below is the memory map of DomU with max mem as 16GB.

for EXTRA_MEM_RATIO  = 1

BIOS-provided physical RAM map:

 Xen: 0000000000000000 - 00000000000a0000 (usable)

 Xen: 00000000000a0000 - 0000000000100000 (reserved)

 Xen: 0000000000100000 - 0000000080000000 (usable)

 Xen: 0000000080000000 - 0000000400000000 (unusable)

NX (Execute Disable) protection: active

DMI not present or invalid.

e820 update range: 0000000000000000 - 0000000000010000 (usable) ==> (reserved)

e820 remove range: 00000000000a0000 - 0000000000100000 (usable)

No AGP bridge found

last_pfn = 0x80000 max_arch_pfn = 0x400000000

initial memory mapped : 0 - 0436c000

Base memory trampoline at [ffff88000009b000] 9b000 size 20480

init_memory_mapping: 0000000000000000-0000000080000000

 0000000000 - 0080000000 page 4k

kernel direct mapping tables up to 80000000 @ bfd000-1000000

xen: setting RW the range fd6000 - 1000000

for EXTRA_MEM_RATIO  = 10 the map is like below and can balloon up to 16GB.

BIOS-provided physical RAM map:

 Xen: 0000000000000000 - 00000000000a0000 (usable)

 Xen: 00000000000a0000 - 0000000000100000 (reserved)

 Xen: 0000000000100000 - 0000000400000000 (usable)

NX (Execute Disable) protection: active

DMI not present or invalid.

e820 update range: 0000000000000000 - 0000000000010000 (usable) ==> (reserved)

e820 remove range: 00000000000a0000 - 0000000000100000 (usable)

No AGP bridge found

last_pfn = 0x400000 max_arch_pfn = 0x400000000

last_pfn = 0x100000 max_arch_pfn = 0x400000000

initial memory mapped : 0 - 0436c000

Base memory trampoline at [ffff88000009b000] 9b000 size 20480

init_memory_mapping: 0000000000000000-0000000100000000

 0000000000 - 0100000000 page 4k

kernel direct mapping tables up to 100000000 @ 7fb000-1000000

xen: setting RW the range fd6000 - 1000000

init_memory_mapping: 0000000100000000-0000000400000000

 0100000000 - 0400000000 page 4k

kernel direct mapping tables up to 400000000 @ 601ef000-62200000

xen: setting RW the range 619fb000 - 62200000

Can someone please help me understand its behavior and importance ?

Thanks.

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