[PATCH V5 16/17] mm: Let arch choose the initial value of task size

[Anshuman Khandual]

On 03/22/2017 09:07 AM, Aneesh Kumar K.V wrote:
> As we start supporting larger address space (>128TB), we want to give
> architecture a control on max task size of an application which is different
> from the TASK_SIZE. For ex: ppc64 needs to track the base page size of a segment
> and it is copied from mm_context_t to PACA on each context switch. If we know that
> application has not used an address range above 128TB we only need to copy
> details about 128TB range to PACA. This will help in improving context switch
> performance by avoiding larger copy operation.
> 
> Cc: Kirill A. Shutemov <kirill.shutemov at linux.intel.com>
> Cc: linux-mm at kvack.org
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
> ---
>  fs/exec.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/exec.c b/fs/exec.c
> index 65145a3df065..5550a56d03c3 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1308,6 +1308,14 @@ void would_dump(struct linux_binprm *bprm, struct file *file)
>  }
>  EXPORT_SYMBOL(would_dump);
>  
> +#ifndef arch_init_task_size
> +static inline void arch_init_task_size(void)
> +{
> +	current->mm->task_size = TASK_SIZE;
> +}
> +#define arch_init_task_size arch_init_task_size
> +#endif

Why not a proper CONFIG_ARCH_DEFINED_TASK_SIZE kind of option for
this ? Also are there no assumptions about task current->mm->size
being TASK_SIZE in other places which might get broken ?