linux-kernel - Re: [RFC PATCH 1/4] mm/mempolicy: Expose policy

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Message-ID: <5a50eeba-b26d-4913-8016-45278608a1ee@redhat.com>
Date: Fri, 13 Jun 2025 15:45:49 +0200
From: David Hildenbrand <david@...hat.com>
To: Bijan Tabatabai <bijan311@...il.com>, damon@...ts.linux.com,
 linux-mm@...ck.org, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: sj@...nel.org, akpm@...ux-foundation.org, corbet@....net, ziy@...dia.com,
 matthew.brost@...el.com, joshua.hahnjy@...il.com, rakie.kim@...com,
 byungchul@...com, gourry@...rry.net, ying.huang@...ux.alibaba.com,
 apopple@...dia.com, bijantabatab@...ron.com, venkataravis@...ron.com,
 emirakhur@...ron.com, ajayjoshi@...ron.com, vtavarespetr@...ron.com
Subject: Re: [RFC PATCH 1/4] mm/mempolicy: Expose policy_nodemask() in
 include/linux/mempolicy.h

On 12.06.25 20:13, Bijan Tabatabai wrote:
> From: Bijan Tabatabai <bijantabatab@...ron.com>
> 
> This patch is to allow DAMON to call policy_nodemask() so it can
> determine where to place a page for interleaving.
> 
> Signed-off-by: Bijan Tabatabai <bijantabatab@...ron.com>
> ---
>   include/linux/mempolicy.h | 9 +++++++++
>   mm/mempolicy.c            | 4 +---
>   2 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
> index 0fe96f3ab3ef..e96bf493ff7a 100644
> --- a/include/linux/mempolicy.h
> +++ b/include/linux/mempolicy.h
> @@ -133,6 +133,8 @@ struct mempolicy *__get_vma_policy(struct vm_area_struct *vma,
>   struct mempolicy *get_vma_policy(struct vm_area_struct *vma,
>   		unsigned long addr, int order, pgoff_t *ilx);
>   bool vma_policy_mof(struct vm_area_struct *vma);
> +nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *pol,
> +		pgoff_t ilx, int *nid);
>   
>   extern void numa_default_policy(void);
>   extern void numa_policy_init(void);
> @@ -232,6 +234,13 @@ static inline struct mempolicy *get_vma_policy(struct vm_area_struct *vma,
>   	return NULL;
>   }
>   
> +static inline nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *pol,
> +				pgoff_t ilx, int *nid)
> +{
> +	*nid = NUMA_NO_NODE;
> +	return NULL;
> +}
> +
>   static inline int
>   vma_dup_policy(struct vm_area_struct *src, struct vm_area_struct *dst)
>   {
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 3b1dfd08338b..54f539497e20 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -596,8 +596,6 @@ static const struct mempolicy_operations mpol_ops[MPOL_MAX] = {
>   
>   static bool migrate_folio_add(struct folio *folio, struct list_head *foliolist,
>   				unsigned long flags);
> -static nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *pol,
> -				pgoff_t ilx, int *nid);
>   
>   static bool strictly_unmovable(unsigned long flags)
>   {
> @@ -2195,7 +2193,7 @@ static unsigned int interleave_nid(struct mempolicy *pol, pgoff_t ilx)
>    * Return a nodemask representing a mempolicy for filtering nodes for
>    * page allocation, together with preferred node id (or the input node id).
>    */
> -static nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *pol,
> +nodemask_t *policy_nodemask(gfp_t gfp, struct mempolicy *pol,
>   				   pgoff_t ilx, int *nid)
>   {
>   	nodemask_t *nodemask = NULL;

You actually only care about the nid for your use case.

Maybe we should add

get_vma_policy_node() that internally does a get_vma_policy() to then 
give you only the node back.

If get_vma_policy() is not the right thing (see my reply to patch #2), 
of course a get_task_policy_node() could be added.

-- 
Cheers,

David / dhildenb