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parisc,metag: Do not hardcode maximum userspace stack size

Message ID 5363876A.2030709@imgtec.com (mailing list archive)
State Not Applicable
Headers show

Commit Message

James Hogan May 2, 2014, 11:54 a.m. UTC
On 01/05/14 18:50, James Bottomley wrote:
> 
>> +
>> +config MAX_STACK_SIZE_MB
>> +	int "Maximum user stack size (MB)"
>> +	default 80
>> +	range 8 256 if METAG
>> +	range 8 2048
>> +	depends on STACK_GROWSUP
>> +	help
>> +	  This is the maximum stack size in Megabytes in the VM layout of user
>> +	  processes when the stack grows upwards (currently only on parisc and
>> +	  metag arch). The stack will be located at the highest memory address
>> +	  minus the given value, unless the RLIMIT_STACK hard limit is changed
>> +	  to a smaller value in which case that is used.
>> +
>> +	  A sane initial value is 80 MB.
> 
> There's one final issue with this: placement of the stack only really
> matters on 32 bits.  We have three expanding memory areas: stack, heap
> and maps.  On 64 bits these are placed well separated from each other on
> 64 bits, so an artificial limit like this doesn't matter.

Does the following fixup diff look reasonable? It forces
MAX_STACK_SIZE_MB to 1024 and hides the Kconfig option for 64BIT,
effectively leaving the behaviour unchanged in that case.


Thanks
James

Comments

James Bottomley May 2, 2014, 2:48 p.m. UTC | #1
On Fri, 2014-05-02 at 12:54 +0100, James Hogan wrote:
> On 01/05/14 18:50, James Bottomley wrote:
> > 
> >> +
> >> +config MAX_STACK_SIZE_MB
> >> +	int "Maximum user stack size (MB)"
> >> +	default 80
> >> +	range 8 256 if METAG
> >> +	range 8 2048
> >> +	depends on STACK_GROWSUP
> >> +	help
> >> +	  This is the maximum stack size in Megabytes in the VM layout of user
> >> +	  processes when the stack grows upwards (currently only on parisc and
> >> +	  metag arch). The stack will be located at the highest memory address
> >> +	  minus the given value, unless the RLIMIT_STACK hard limit is changed
> >> +	  to a smaller value in which case that is used.
> >> +
> >> +	  A sane initial value is 80 MB.
> > 
> > There's one final issue with this: placement of the stack only really
> > matters on 32 bits.  We have three expanding memory areas: stack, heap
> > and maps.  On 64 bits these are placed well separated from each other on
> > 64 bits, so an artificial limit like this doesn't matter.
> 
> Does the following fixup diff look reasonable? It forces
> MAX_STACK_SIZE_MB to 1024 and hides the Kconfig option for 64BIT,
> effectively leaving the behaviour unchanged in that case.
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index e80075979530..b0307f737bd7 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -583,7 +583,8 @@ config GENERIC_EARLY_IOREMAP
>  	bool
> 
>  config MAX_STACK_SIZE_MB
> -	int "Maximum user stack size (MB)"
> +	int "Maximum user stack size (MB)" if !64BIT
> +	default 1024 if 64BIT
>  	default 80
>  	range 8 256 if METAG
>  	range 8 2048

Yes, I think that's probably correct ... parisc doesn't actually have
anything other than a testbed 64 bit userspace, so this is a bit
theoretical for us.

James


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Helge Deller May 4, 2014, 7:28 a.m. UTC | #2
On 05/02/2014 04:48 PM, James Bottomley wrote:
> On Fri, 2014-05-02 at 12:54 +0100, James Hogan wrote:
>> On 01/05/14 18:50, James Bottomley wrote:
>>>
>>>> +
>>>> +config MAX_STACK_SIZE_MB
>>>> +	int "Maximum user stack size (MB)"
>>>> +	default 80
>>>> +	range 8 256 if METAG
>>>> +	range 8 2048
>>>> +	depends on STACK_GROWSUP
>>>> +	help
>>>> +	  This is the maximum stack size in Megabytes in the VM layout of user
>>>> +	  processes when the stack grows upwards (currently only on parisc and
>>>> +	  metag arch). The stack will be located at the highest memory address
>>>> +	  minus the given value, unless the RLIMIT_STACK hard limit is changed
>>>> +	  to a smaller value in which case that is used.
>>>> +
>>>> +	  A sane initial value is 80 MB.
>>>
>>> There's one final issue with this: placement of the stack only really
>>> matters on 32 bits.  We have three expanding memory areas: stack, heap
>>> and maps.  On 64 bits these are placed well separated from each other on
>>> 64 bits, so an artificial limit like this doesn't matter.
>>
>> Does the following fixup diff look reasonable? It forces
>> MAX_STACK_SIZE_MB to 1024 and hides the Kconfig option for 64BIT,
>> effectively leaving the behaviour unchanged in that case.
>>
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index e80075979530..b0307f737bd7 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -583,7 +583,8 @@ config GENERIC_EARLY_IOREMAP
>>  	bool
>>
>>  config MAX_STACK_SIZE_MB
>> -	int "Maximum user stack size (MB)"
>> +	int "Maximum user stack size (MB)" if !64BIT
>> +	default 1024 if 64BIT
>>  	default 80
>>  	range 8 256 if METAG
>>  	range 8 2048
> 
> Yes, I think that's probably correct ... 

No, it's not correct.
It will then choose then a 1GB stack for compat tasks on 64bit kernel.

Helge

> parisc doesn't actually have
> anything other than a testbed 64 bit userspace, so this is a bit
> theoretical for us.




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diff mbox

Patch

diff --git a/mm/Kconfig b/mm/Kconfig
index e80075979530..b0307f737bd7 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -583,7 +583,8 @@  config GENERIC_EARLY_IOREMAP
 	bool

 config MAX_STACK_SIZE_MB
-	int "Maximum user stack size (MB)"
+	int "Maximum user stack size (MB)" if !64BIT
+	default 1024 if 64BIT
 	default 80
 	range 8 256 if METAG
 	range 8 2048