Re: [PATCH 4/4] Swap migration V3: sys_migrate_pages interface

[Simon Derr]

On Fri, 21 Oct 2005, KAMEZAWA Hiroyuki wrote:

> 
> Christoph Lameter wrote:
> > +	/* Is the user allowed to access the target nodes? */
> > +	if (!nodes_subset(new, cpuset_mems_allowed(task)))
> > +		return -EPERM;
> > +
> How about this ?
> +cpuset_update_task_mems_allowed(task, new);    (this isn't implemented now)
> 
> > +	err = do_migrate_pages(mm, &old, &new, MPOL_MF_MOVE);
> > +
> 
> or it's user's responsibility  to updates his mempolicy before
> calling sys_migrage_pages() ?
> 

The user cannot always add a memory node to a cpuset, for example if this 
cpuset is inside another cpuset that is owned by another user. (i.e the 
case where the administrator wants to dedicate a part of the machine to a 
user).

The kernel checks for these permission issues, conflicts with other 
mem_exclusive cpusets, etc... when you write in the 'mems' file.

Automatically updating the ->mems_allowed field as you suggest would 
require that the kernel do the same checks in sys_migrage_pages(). Sounds 
not as a very good idea to me.

	Simon.

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