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Re: [Qemu-devel] [PATCH] configure: Support system emulation with large


From: Blue Swirl
Subject: Re: [Qemu-devel] [PATCH] configure: Support system emulation with large memory on w32 hosts
Date: Mon, 23 Jul 2012 18:32:42 +0000

On Fri, Jul 20, 2012 at 5:19 PM, Stefan Weil <address@hidden> wrote:
> Am 20.07.2012 08:38, schrieb Alexey Kardashevskiy:
>
>> On 20/07/12 16:05, Alexey Kardashevskiy wrote:
>>>
>>> On 20/07/12 15:37, Alexey Kardashevskiy wrote:
>>>>
>>>> On 20/07/12 15:23, Stefan Weil wrote:
>>>>>
>>>>> Am 20.07.2012 05:53, schrieb Alexey Kardashevskiy:
>>>>>>
>>>>>> On 19/07/12 02:37, Stefan Weil wrote:
>>>>>>>
>>>>>>> 32-bit applications on Windows normally only get virtual memory in
>>>>>>> the lower 2 GiB address space.
>>>>>>>
>>>>>>> Because of memory fragmentation, VirtualAlloc() usually won't get 1
>>>>>>> GiB
>>>>>>> of contiguous virtual memory in that address space. Therefore running
>>>>>>> system emulations with 1 GiB or more RAM will abort with a failure.
>>>>>>>
>>>>>>> The linker flag --large-address-aware allows addresses in the upper 2
>>>>>>> GiB.
>>>>>>> With this flag, it is possible to run emulated machines with up to
>>>>>>> 2047 MiB RAM.
>>>>>>>
>>>>>>> Signed-off-by: Stefan Weil<address@hidden>
>>>>>>> ---
>>>>>>>
>>>>>>> I tested the executables with large address awareness on a 64 bit
>>>>>>> Windows
>>>>>>> (works) and with Wine on Debian 32 bit Linux (no longer aborts, but
>>>>>>> hangs
>>>>>>> when 1024 or more MiB are requested).
>>>>>>>
>>>>>>> Maybe the support for large addresses is broken in my Wine version.
>>>>>>> Please report any different test results.
>>>>>>
>>>>>>
>>>>>> I tried with native WindowsXP, the patch did not help.
>>>>>>
>>>>>> QEMU was compiled with the new parameter:
>>>>>>
>>>>>> Install prefix    c:/Program Files/QEMU
>>>>>> BIOS directory    c:/Program Files/QEMU
>>>>>> binary directory  c:/Program Files/QEMU
>>>>>> library directory c:/Program Files/QEMU/lib
>>>>>> include directory c:/Program Files/QEMU/include
>>>>>> config directory  c:/Program Files/QEMU
>>>>>> Source path       /home/aik/testken/qemu
>>>>>> C compiler        i686-pc-mingw32-gcc
>>>>>> Host C compiler   gcc
>>>>>> CFLAGS            -O2 -D_FORTIFY_SOURCE=2 -g
>>>>>> QEMU_CFLAGS       -m32 -D__USE_MINGW_ANSI_STDIO=1
>>>>>> -DWIN32_LEAN_AND_MEAN
>>>>>> -DWINVER=0x501 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64
>>>>>> -D_LARGEFILE_SOURCE
>>>>>> -Wstrict-prototypes -Wredundant-decls -Wall -Wundef -Wwrite-strings
>>>>>> -Wmissing-prototypes -fno-strict-aliasing  -fstack-protector-all
>>>>>> -Wendif-labels -Wmissing-include-dirs -Wempty-body -Wnested-externs
>>>>>> -Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers
>>>>>> -Wold-style-declaration -Wold-style-definition -Wtype-limits
>>>>>> LDFLAGS           -Wl,--nxcompat -Wl,--no-seh
>>>>>> -Wl,--large-address-aware
>>>>>> -Wl,--dynamicbase -Wl,--warn-common -m32 -static -g
>>>>>> make              make
>>>>>> install           install
>>>>>> python            python
>>>>>> smbd              /usr/sbin/smbd
>>>>>> host CPU          i386
>>>>>> host big endian   no
>>>>>> target list       ppc64-softmmu
>>>>>> [...]
>>>>>>
>>>>>>
>>>>>>
>>>>>> qemu/ppc64-softmmu/qemu-system-ppc64 -M pseries -m 1024 -nographic -L
>>>>>> qemu/pc-bios/ -net none -append console=hvc0 -initrd ./1.cpio -kernel
>>>>>> ./guest.vmlinux.n -net nic,model=virtio -net
>>>>>> user,hostfwd=tcp::5555-:22
>>>>>> -drive
>>>>>> file=test-virtio-blk.img,if=virtio,index=0,media=disk,cache=unsafe
>>>>>> ***qemu_memalign 200 (512) size 800 (2048)
>>>>>> Warning: Disabling some instructions which are not emulated by TCG
>>>>>> (0x0, 0x6)
>>>>>> ***qemu_vmalloc 40000000 (1073741824)
>>>>>> Failed to allocate memory: 8
>>>>>>
>>>>>> This application has requested the Runtime to terminate it in an
>>>>>> unusual way.
>>>>>> Please contact the application's support team for more information.
>>>>>>
>>>>>>
>>>>>> The lines with *** are mine printf("%s %x(%u)", __func__, etc).
>>>>>>
>>>>>> It still works with "-m 1023".
>>>>>
>>>>>
>>>>> Do you have enough RAM? Even with 64 bit Windows 7, I am
>>>>> limited to -m 7000 with 64 bit QEMU on a 8 GiB host.
>>>>> 32 bit QEMU runs there with up to 2047 MiB.
>>>>
>>>>
>>>>
>>>> I put another VirtualAlloc(64MB) call in qemu_vmalloc(1023MB) to check
>>>> if
>>>> it fails but it did not so it is possible to allocate 1087MB but in 2
>>>> pieces.
>>>>
>>>>
>>>>> On 32 bit Windows XP, I'd expect that you need 2 GiB (or better
>>>>> 3 GiB) of physical RAM in your host, and close all other
>>>>> programs before you try QEMU.
>>>>
>>>>
>>>> How do other programs matter? It is virtual 2GB per process, no?
>>>> Ah, anyway, it has 2.994.340KB of physical RAM, swapping is enabled, the
>>>> task manager shows at least "2000000" in "Available", one cygwin shell
>>>> is
>>>> running.
>>>> And QEMU can always alloc 1023MB (in one chunk) and never 1024MB (also
>>>> in
>>>> one chunk). For me it looks like XP limitation but I could not find any
>>>> mention of it in MSDN.
>>>>
>>>>
>>>>> Maybe I can run a test with Windows XP during the weekend.
>>>>>
>>>>> By the way: the patch must be modified to work for 64 bit QEMU.
>>>>> MinGW-w64's ld shows the new parameter in its help, but does
>>>>> not support it for 64 bit executables.
>>>>
>>>>
>>>>
>>>> Not sure if I understood :)
>>>> The compiler I use is "i686-pc-mingw32-gcc -m32", target is
>>>> ppc64-softmmu.
>>>>
>>>>
>>>
>>> Did a simple test inside QEMU, ran it twice:
>>>
>>> run#1: first alloc 64MB, then 1023MB - failed.
>>> va(0x4000000) ->  ptr=1d0d0000, last error = 0
>>> va(0x3FF00000) ->  ptr=00000000, last error = 8
>>>
>>> run#2: first alloc 1023MB, then 64MB - succeeded.
>>> va(0x3FF00000) ->  ptr=1d0d0000, last error = 0
>>> va(0x4000000) ->  ptr=5d130000, last error = 0
>>>
>>> As we can see, there is 340000h gap between 2 chunks.
>>>
>>> Have no idea what that means :) May be something is wrong with my
>>> machine,
>>> dunno.
>>
>>
>> Looked further, c:\windows\system32\sysctl32.dll is mapped there so there
>> is just no big chunk of RAM. But still there is some RAM, it is just
>> fragmented.
>
>
> Yes, that's the problem: the QEMU executable and all the DLLs
> occupy RAM in the range from 0 to 2 GiB, so this area is very
> fragmented and it's impossible to get a large contiguous memory
> area (which VirtualAlloc requires!).

I think the real fix is to implement guest RAM using DIMMs slots so
that either one contiguous block can be used for all DIMMs (for huge
page table benefits on Linux) or several host memory blocks can be
used, one for each DIMM (for Windows).

>
> On 64 bit Windows, addresses from 2 GiB to 4 GiB can be used
> with --large-address-aware, so there is no such problem.
> With 64 bit executables, even more RAM above 4 GiB is available.
>
> If you have enough RAM, you can configure a 32 bit Windows to
> provide 3 GiB instead of 2 GiB to user applications. This
> non-standard configuration also allows larger sizes for VirtualAlloc.
>
> See
> http://msdn.microsoft.com/en-us/library/windows/desktop/aa366778%28v=vs.85%29.aspx
>
> for more information.
>
> See http://qemu.weilnetz.de/w32/virtualalloc-test/ for a simple test
> program.
>
> Regards,
>
> Stefan Weil
>
>



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