Re: [PATCH] parisc,metag: Do not hardcode maximum userspace stack size

James Hogan
2014-05-02T11:54:29Z

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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

Thanks
James

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