* The limit of kernel memory in 64bit system
@ 2014-11-28 15:25 J.Hwan Kim
2014-11-29 17:45 ` Greg KH
0 siblings, 1 reply; 6+ messages in thread
From: J.Hwan Kim @ 2014-11-28 15:25 UTC (permalink / raw)
To: kernelnewbies
Hi, everyone
As far as I know, the kernel memory limit is 1GB in 32bit system.
Is it also applicable to 64bit system?
What's the limit of kernel memory in 64bit system?
Thanks in advance
Regards,
J.Hwan Kim
^ permalink raw reply [flat|nested] 6+ messages in thread
* The limit of kernel memory in 64bit system
2014-11-28 15:25 The limit of kernel memory in 64bit system J.Hwan Kim
@ 2014-11-29 17:45 ` Greg KH
2014-11-29 19:16 ` nick
0 siblings, 1 reply; 6+ messages in thread
From: Greg KH @ 2014-11-29 17:45 UTC (permalink / raw)
To: kernelnewbies
On Sat, Nov 29, 2014 at 12:25:43AM +0900, J.Hwan Kim wrote:
> Hi, everyone
>
> As far as I know, the kernel memory limit is 1GB in 32bit system.
> Is it also applicable to 64bit system?
> What's the limit of kernel memory in 64bit system?
There is no limit :)
What do you really want to know this for?
greg k-h
^ permalink raw reply [flat|nested] 6+ messages in thread
* The limit of kernel memory in 64bit system
2014-11-29 17:45 ` Greg KH
@ 2014-11-29 19:16 ` nick
2014-11-29 20:54 ` Yiqun Chen
0 siblings, 1 reply; 6+ messages in thread
From: nick @ 2014-11-29 19:16 UTC (permalink / raw)
To: kernelnewbies
J.Hwan,
There is a limit as 64 bit can only support 16 extabytes. Greg is right in that there is no real limit
on modern machines because of this. However from my knowledge, system ram is split into a 3 to 1 ratio,
where 75 percent is for user space and the only quarter is for the kernel's memory. So on my system with
8 GB of ram, the kernel can use up to 25 percent or 2 GB of ram.
Hope this answers your question,
Nick
On 2014-11-29 12:45 PM, Greg KH wrote:
> On Sat, Nov 29, 2014 at 12:25:43AM +0900, J.Hwan Kim wrote:
>> Hi, everyone
>>
>> As far as I know, the kernel memory limit is 1GB in 32bit system.
>> Is it also applicable to 64bit system?
>> What's the limit of kernel memory in 64bit system?
>
> There is no limit :)
>
> What do you really want to know this for?
>
> greg k-h
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* The limit of kernel memory in 64bit system
2014-11-29 19:16 ` nick
@ 2014-11-29 20:54 ` Yiqun Chen
2014-11-29 22:35 ` nick
0 siblings, 1 reply; 6+ messages in thread
From: Yiqun Chen @ 2014-11-29 20:54 UTC (permalink / raw)
To: kernelnewbies
Incorrect. The 64 bit machine theoretically supports 2 ^ 64 bytes virtual
memory space but on x86 only 48 out of 64 address buses are used. So we
cannot assume the upper limit of physical space.on different platforms.
And Nick you're confusing with the physical and virtual memory. The usage
of memory for kernel space is not determined by the ratio. It's defined by
mapping strategy. You first need to know why this 3 to 1 was used. It's
because we cannot map all the physical pages onto the corresponding virtual
address since we need to spare some linear space for user program. But on
64 bits platform we have plenty virtual address for the programmer as the
physical memory is much much smaller than it. On x86_64 we divide
kernel/user space by setting all the first 16 bits with 0 or 1 as the user
or kernel space respectfully. So how large would the kernel space be if we
could use 48-bit linear space?
On Sat, Nov 29, 2014 at 8:16 PM, nick <xerofoify@gmail.com> wrote:
> J.Hwan,
> There is a limit as 64 bit can only support 16 extabytes. Greg is right in
> that there is no real limit
> on modern machines because of this. However from my knowledge, system ram
> is split into a 3 to 1 ratio,
> where 75 percent is for user space and the only quarter is for the
> kernel's memory. So on my system with
> 8 GB of ram, the kernel can use up to 25 percent or 2 GB of ram.
> Hope this answers your question,
> Nick
> On 2014-11-29 12:45 PM, Greg KH wrote:
> > On Sat, Nov 29, 2014 at 12:25:43AM +0900, J.Hwan Kim wrote:
> >> Hi, everyone
> >>
> >> As far as I know, the kernel memory limit is 1GB in 32bit system.
> >> Is it also applicable to 64bit system?
> >> What's the limit of kernel memory in 64bit system?
> >
> > There is no limit :)
> >
> > What do you really want to know this for?
> >
> > greg k-h
> >
> > _______________________________________________
> > Kernelnewbies mailing list
> > Kernelnewbies at kernelnewbies.org
> > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> >
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
--
Best regards
Chen, Yiqun
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* The limit of kernel memory in 64bit system
2014-11-29 20:54 ` Yiqun Chen
@ 2014-11-29 22:35 ` nick
2014-12-01 18:35 ` Christoph Lameter
0 siblings, 1 reply; 6+ messages in thread
From: nick @ 2014-11-29 22:35 UTC (permalink / raw)
To: kernelnewbies
Sorry Yiqun,
I was thinking of virtual memory so you are correct. I also haven't looked into
the kernel memory subsystem(s) in a while so I may be a little behind in my knownledge
of them.
Regards Nick
On 2014-11-29 03:54 PM, Yiqun Chen wrote:
> Incorrect. The 64 bit machine theoretically supports 2 ^ 64 bytes virtual
> memory space but on x86 only 48 out of 64 address buses are used. So we
> cannot assume the upper limit of physical space.on different platforms.
> And Nick you're confusing with the physical and virtual memory. The usage
> of memory for kernel space is not determined by the ratio. It's defined by
> mapping strategy. You first need to know why this 3 to 1 was used. It's
> because we cannot map all the physical pages onto the corresponding virtual
> address since we need to spare some linear space for user program. But on
> 64 bits platform we have plenty virtual address for the programmer as the
> physical memory is much much smaller than it. On x86_64 we divide
> kernel/user space by setting all the first 16 bits with 0 or 1 as the user
> or kernel space respectfully. So how large would the kernel space be if we
> could use 48-bit linear space?
>
> On Sat, Nov 29, 2014 at 8:16 PM, nick <xerofoify@gmail.com> wrote:
>
>> J.Hwan,
>> There is a limit as 64 bit can only support 16 extabytes. Greg is right in
>> that there is no real limit
>> on modern machines because of this. However from my knowledge, system ram
>> is split into a 3 to 1 ratio,
>> where 75 percent is for user space and the only quarter is for the
>> kernel's memory. So on my system with
>> 8 GB of ram, the kernel can use up to 25 percent or 2 GB of ram.
>> Hope this answers your question,
>> Nick
>> On 2014-11-29 12:45 PM, Greg KH wrote:
>>> On Sat, Nov 29, 2014 at 12:25:43AM +0900, J.Hwan Kim wrote:
>>>> Hi, everyone
>>>>
>>>> As far as I know, the kernel memory limit is 1GB in 32bit system.
>>>> Is it also applicable to 64bit system?
>>>> What's the limit of kernel memory in 64bit system?
>>>
>>> There is no limit :)
>>>
>>> What do you really want to know this for?
>>>
>>> greg k-h
>>>
>>> _______________________________________________
>>> Kernelnewbies mailing list
>>> Kernelnewbies at kernelnewbies.org
>>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>>
>>
>> _______________________________________________
>> Kernelnewbies mailing list
>> Kernelnewbies at kernelnewbies.org
>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>
>
>
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* The limit of kernel memory in 64bit system
2014-11-29 22:35 ` nick
@ 2014-12-01 18:35 ` Christoph Lameter
0 siblings, 0 replies; 6+ messages in thread
From: Christoph Lameter @ 2014-12-01 18:35 UTC (permalink / raw)
To: kernelnewbies
On Sat, 29 Nov 2014, nick wrote:
> Sorry Yiqun,
> I was thinking of virtual memory so you are correct. I also haven't looked into
> the kernel memory subsystem(s) in a while so I may be a little behind in my knownledge
> of them.
2^1
The amount of memory that can be handled by a processor is available via
/proc/cpuinfo:
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 60
model name : Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz
stepping : 3
microcode : 0x16
cpu MHz : 3400.132
cache size : 8192 KB
clflush size : 64
cache_alignment : 64
address sizes : 39 bits physical, 48 bits virtual
so this processor support a physical memory space of 2^39 = 512GB and a
virtual address space of 256 TB.
A 64 bit kernel can support what the processor supports.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2014-11-28 15:25 The limit of kernel memory in 64bit system J.Hwan Kim
2014-11-29 17:45 ` Greg KH
2014-11-29 19:16 ` nick
2014-11-29 20:54 ` Yiqun Chen
2014-11-29 22:35 ` nick
2014-12-01 18:35 ` Christoph Lameter
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