Re: [PATCH/RFC] 2.6.23-rc1-mm1: MPOL_PREFERRED fixups for preferred_node < 0

[mel@skynet.ie (Mel Gorman)]

On (30/07/07 18:00), Lee Schermerhorn didst pronounce:
> On Mon, 2007-07-30 at 17:38 -0400, Lee Schermerhorn wrote:
> > These are some "issues" that I came across working on the Memoryless
> > Node series.  I'm using the same cc: list as that series as the issues
> > are somewhat related.
> > 
> > Only boot tested at this point.
> 
> I sent the wrong patch--forgot to refresh before posting :-(.  Bogus
> code in mpol_to_str() in previous patch.
> 
> Try this one.
> 
> Lee
> 
> > ---------------------------
> 
> PATCH/RFC - MPOL_PREFERRED fixups for "local allocation"
> 
> Here are a couple of potential "fixups" for MPOL_PREFERRED behavior
> when v.preferred_node < 0 -- i.e., "local allocation":
> 
> 1)  [do_]get_mempolicy() calls the misnamed get_zonemask() to fetch the
>     nodemask associated with a policy.  Currently, get_zonemask() returns
>     the set of nodes with memory, when the policy 'mode' is 'PREFERRED,

Consider a cleanup that renames get_zonemask because the naming is
misleading.

>     and the preferred_node is < 0.  Return the set of allowed nodes
>     instead.  This will already have been masked to include only nodes
>     with memory.
> 
> 2)  When a task is moved into a [new] cpuset, mpol_rebind_policy() is
>     called to adjust any task and vma policy nodes to be valid in the
>     new cpuset.  However, when the policy is MPOL_PREFERRED, and the
>     preferred_node is <0, no rebind is necessary.  The "local allocation"
>     indication is valid in any cpuset.
> 
> 3)  mpol_to_str() produces a printable, "human readable" string from a
>     struct mempolicy.  For MPOL_PREFERRED with preferred_node <0,  show
>     the entire set of valid nodes.  Although, technically, MPOL_PREFERRED
>     takes only a single node, preferred_node <0 is a local allocation policy,
>     with the preferred node determined by the context where the task
>     is executing.  All of the allowed nodes are possible, as the task
>     migrates amoung the nodes in the cpuset.
> 
> Comments?
> 
> Signed-off-by:  Lee Schermerhorn <lee.schermerhorn@hp.com>
> 
>  mm/mempolicy.c |   31 ++++++++++++++++++++++++-------
>  1 file changed, 24 insertions(+), 7 deletions(-)
> 
> Index: Linux/mm/mempolicy.c
> ===================================================================
> --- Linux.orig/mm/mempolicy.c	2007-07-30 17:32:06.000000000 -0400
> +++ Linux/mm/mempolicy.c	2007-07-30 17:38:17.000000000 -0400
> @@ -494,9 +494,11 @@ static void get_zonemask(struct mempolic
>  		*nodes = p->v.nodes;
>  		break;
>  	case MPOL_PREFERRED:
> -		/* or use current node instead of memory_map? */
> +		/*
> +		 * for "local policy", return allowed memories
> +		 */
>  		if (p->v.preferred_node < 0)
> -			*nodes = node_states[N_MEMORY];
> +			*nodes = cpuset_current_mems_allowed;
>  		else

Is this actually a bugfix? From this context, it looks like memory
policies using MPOL_PREFERRED can ignore cpusets.

>  			node_set(p->v.preferred_node, *nodes);
>  		break;
> @@ -1650,6 +1652,7 @@ void mpol_rebind_policy(struct mempolicy
>  {
>  	nodemask_t *mpolmask;
>  	nodemask_t tmp;
> +	int nid;
>  
>  	if (!pol)
>  		return;
> @@ -1668,9 +1671,15 @@ void mpol_rebind_policy(struct mempolicy
>  						*mpolmask, *newmask);
>  		break;
>  	case MPOL_PREFERRED:
> -		pol->v.preferred_node = node_remap(pol->v.preferred_node,
> +		/*
> +		 * no need to remap "local policy"
> +		 */
> +		nid = pol->v.preferred_node;
> +		if (nid >= 0) {
> +			pol->v.preferred_node = node_remap(nid,
>  						*mpolmask, *newmask);
> -		*mpolmask = *newmask;
> +			*mpolmask = *newmask;
> +		}
>  		break;
>  	case MPOL_BIND: {
>  		nodemask_t nodes;
> @@ -1745,7 +1754,7 @@ static const char * const policy_types[]
>  static inline int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
>  {
>  	char *p = buffer;
> -	int l;
> +	int nid, l;
>  	nodemask_t nodes;
>  	int mode = pol ? pol->policy : MPOL_DEFAULT;
>  
> @@ -1755,8 +1764,16 @@ static inline int mpol_to_str(char *buff
>  		break;
>  
>  	case MPOL_PREFERRED:
> -		nodes_clear(nodes);
> -		node_set(pol->v.preferred_node, nodes);
> +		nid = pol->v.preferred_node;
> +		/*
> +		 * local interleave, show all valid nodes
> +		 */
> +		if (nid < 0 )
> +			nodes = cpuset_current_mems_allowed;
> +		else {
> +			nodes_clear(nodes);
> +			node_set(nid, nodes);
> +		}
>  		break;
>  
>  	case MPOL_BIND:
> 

-- 
-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab

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