Re: [Qemu-devel] Memory: how to determine the max memory size of one VM?

[Zhi Yong Wu]

On Fri, Feb 10, 2012 at 7:10 PM, Stefan Hajnoczi <address@hidden> wrote:
> On Fri, Feb 10, 2012 at 11:00 AM, Zhi Yong Wu <address@hidden> wrote:
>> On Fri, Feb 10, 2012 at 6:35 PM, Stefan Hajnoczi <address@hidden> wrote:
>>> On Fri, Feb 10, 2012 at 9:47 AM, Zhi Yong Wu <address@hidden> wrote:
>>>> Today i tried to create one VM with the option "-m 4000", and found it
>>>> failed with the following errors:
>>>>
>>>> Failed to allocate 4194304000 B: Cannot allocate memory
>>>> Aborted (core dumped)
>>>
>>> Did you run on a 32-bit host?
>> No, it is one x86_64 host.
>
> That is weird.  Have you tried strace(1) to find out which system call
> is failing and why?
It seems that it failed to call mmap().  ENOMEM

mprotect(0x7fdd5f973000, 4096, PROT_NONE) = 0
clone(child_stack=0x7fdd60172eb0,
flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID,
parent_tidptr=0x7fdd601739d0, tls=0x7fdd60173700,
child_tidptr=0x7fdd601739d0) = 25488
rt_sigprocmask(SIG_SETMASK, [BUS ALRM IO RT_6], NULL, 8) = 0
select(11, [10], [], NULL, NULL)        = 1 (in [10])
read(10, "\0", 16)                      = 1
close(9)                                = 0
open("/home/zwu/work/misc/rh6.img", O_RDONLY|O_NONBLOCK) = 9
fstat(9, {st_mode=S_IFREG|0644, st_size=1396244480, ...}) = 0
close(9)                                = 0
open("/home/zwu/work/misc/rh6.img", O_RDONLY|O_NONBLOCK) = 9
fstat(9, {st_mode=S_IFREG|0644, st_size=1396244480, ...}) = 0
close(9)                                = 0
stat("/home/zwu/work/misc/rh6.img", {st_mode=S_IFREG|0644,
st_size=1396244480, ...}) = 0
open("/home/zwu/work/misc/rh6.img", O_RDWR|O_DSYNC|O_CLOEXEC) = 9
lseek(9, 0, SEEK_END)                   = 1396244480
futex(0x7fdd67c6e724, FUTEX_WAKE_OP_PRIVATE, 1, 1, 0x7fdd67c6e720,
{FUTEX_OP_SET, 0, FUTEX_OP_CMP_GT, 1}) = 1
select(11, [10], [], NULL, NULL)        = 1 (in [10])
read(10, "\0", 16)                      = 1
lseek(9, 0, SEEK_END)                   = 1396244480
mmap(NULL, 266240, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0x7fdd670d1000
write(7, "\1\0\0\0\0\0\0\0", 8)         = 8
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [BUS ALRM IO RT_6], 8) = 0
mmap(NULL, 8392704, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x7fdd5f172000
mprotect(0x7fdd5f172000, 4096, PROT_NONE) = 0
clone(child_stack=0x7fdd5f971eb0,
flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID,
parent_tidptr=0x7fdd5f9729d0, tls=0x7fdd5f972700,
child_tidptr=0x7fdd5f9729d0) = 25489
rt_sigprocmask(SIG_SETMASK, [BUS ALRM IO RT_6], NULL, 8) = 0
select(11, [10], [], NULL, NULL)        = 1 (in [10])
read(10, "\0", 16)                      = 1
write(7, "\1\0\0\0\0\0\0\0", 8)         = 8
brk(0)                                  = 0x7fdd68f1a000
brk(0x7fdd68f3b000)                     = 0x7fdd68f3b000
open("/proc/meminfo", O_RDONLY)         = 12
fstat(12, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0x7fdd67243000
read(12, "MemTotal:        2019156 kB\nMemF"..., 1024) = 1024
close(12)                               = 0
munmap(0x7fdd67243000, 4096)            = 0
getrlimit(RLIMIT_NOFILE, {rlim_cur=1024, rlim_max=4*1024}) = 0
gettid()                                = 25462
rt_sigprocmask(SIG_SETMASK, ~[RTMIN RT_1], [BUS ALRM IO RT_6], 8) = 0
mmap(NULL, 8392704, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x7fdd5e971000
mprotect(0x7fdd5e971000, 4096, PROT_NONE) = 0
clone(child_stack=0x7fdd5f170eb0,
flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID,
parent_tidptr=0x7fdd5f1719d0, tls=0x7fdd5f171700,
child_tidptr=0x7fdd5f1719d0) = 25490
rt_sigprocmask(SIG_SETMASK, [BUS ALRM IO RT_6], NULL, 8) = 0
futex(0x7fdd67c8efc4, FUTEX_WAIT_PRIVATE, 1, NULL) = 0
mmap(NULL, 4196405248, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = -1 ENOMEM (Cannot allocate memory)
brk(0)                                  = 0x7fdd68f3b000
brk(0x7fde63158000)                     = 0x7fdd68f3b000
mmap(NULL, 4196536320, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = -1 ENOMEM (Cannot allocate memory)
mmap(NULL, 134217728, PROT_NONE,
MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE, -1, 0) = 0x7fdd50000000
munmap(0x7fdd54000000, 67108864)        = 0
mprotect(0x7fdd50000000, 135168, PROT_READ|PROT_WRITE) = 0
mmap(NULL, 4196405248, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = -1 ENOMEM (Cannot allocate memory)
write(2, "Failed to allocate 4194304000 B:"..., 56Failed to allocate
4194304000 B: Cannot allocate memory
) = 56
rt_sigprocmask(SIG_UNBLOCK, [ABRT], NULL, 8) = 0
tgkill(25462, 25462, SIGABRT)           = 0
--- {si_signo=SIGABRT, si_code=SI_TKILL, si_pid=25462, si_uid=0,
si_value={int=1667424088, ptr=0xffff88006362df58}} (Aborted) ---
+++ killed by SIGABRT (core dumped) +++
Aborted (core dumped)

>
>>> until you begin dirtying more host pages than the host has resources
>>> for.
>>>
>>> But normally for KVM you want sum(vms) < host_ram, unless you are
>> here host_ram is the free ram of host?
>
> I meant that for predictable, good performance it is normal to size
> hosts so they have more physical RAM than the sum of guest RAM.
>
> For example, 2 GB VM and 4 GB VM => make sure you have more than 6 GB
> RAM.  If you go under that threshold you will hit swap when the guests
> utilize their memory.
>
> Stefan



-- 
Regards,

Zhi Yong Wu