Re: [RFC PATCH 2/4] mm/damon/paddr: Add DAMOS_INTERLEAVE action

[David Hildenbrand]

On 12.06.25 20:13, Bijan Tabatabai wrote:
> From: Bijan Tabatabai <bijantabatab@xxxxxxxxxx>
>
> This patch adds the DAMOS_INTERLEAVE action.
> It interleaves pages inside of a given region according to the weights
> in the iw_table. To reuse existing interleaving code, the target nid for
> a folio is determined by calling policy_nodemask, therefore only folios
> belonging to processes using the MPOL_WEIGHTED_INTERLEAVE policy will
> have their pages migrated.
>
> Below is an example of its usage where pages are initially interleaved at
> a 1:1 ratio and then changed to be interleaved at a 2:1 ratio. The
> alloc_data program simply allocates 1GB of data then sleeps.
>    $ cd /sys/kernel/mm/damon/admin/kdamonds/0
>    $ sudo cat ./contexts/0/schemes/0/action
>    interleave
>    $ echo 1 | sudo tee /sys/kernel/mm/mempolicy/weighted_interleave/node0
>    $ echo 1 | sudo tee /sys/kernel/mm/mempolicy/weighted_interleave/node1
>    $ numactl -w 0,1 ~/alloc_data 1G &
>    $ numastat -c -p alloc_data
>
>    Per-node process memory usage (in MBs) for PID 18473 (alloc_data)
>             Node 0 Node 1 Total
>             ------ ------ -----
>    Huge          0      0     0
>    Heap          0      0     0
>    Stack         0      0     0
>    Private     514    514  1027
>    -------  ------ ------ -----
>    Total       514    514  1028
>    $ echo 2 | sudo tee /sys/kernel/mm/mempolicy/weighted_interleave/node0
>    $ numastat -c -p alloc_data
>
>    Per-node process memory usage (in MBs) for PID 18473 (alloc_data)
>             Node 0 Node 1 Total
>             ------ ------ -----
>    Huge          0      0     0
>    Heap          0      0     0
>    Stack         0      0     0
>    Private     684    343  1027
>    -------  ------ ------ -----
>    Total       684    343  1027
>
> Signed-off-by: Bijan Tabatabai <bijantabatab@xxxxxxxxxx>
> ---
>   Documentation/mm/damon/design.rst |   2 +
>   include/linux/damon.h             |   2 +
>   mm/damon/paddr.c                  | 112 ++++++++++++++++++++++++++++++
>   mm/damon/sysfs-schemes.c          |   1 +
>   4 files changed, 117 insertions(+)
>
> diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst
> index ddc50db3afa4..c50d2105cea0 100644
> --- a/Documentation/mm/damon/design.rst
> +++ b/Documentation/mm/damon/design.rst
> @@ -455,6 +455,8 @@ that supports each action are as below.
>      Supported by ``paddr`` operations set.
>    - ``migrate_cold``: Migrate the regions prioritizing colder regions.
>      Supported by ``paddr`` operations set.
> + - ``interleave``: Interleave the regions according to the weighted interleave weights.
> +   Supported by ``paddr`` operations set.
>    - ``stat``: Do nothing but count the statistics.
>      Supported by all operations sets.
>   
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index a4011726cb3b..81d26a203337 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -117,6 +117,7 @@ struct damon_target {
>    * @DAMOS_LRU_DEPRIO:	Deprioritize the region on its LRU lists.
>    * @DAMOS_MIGRATE_HOT:  Migrate the regions prioritizing warmer regions.
>    * @DAMOS_MIGRATE_COLD:	Migrate the regions prioritizing colder regions.
> + * @DAMOS_INTERLEAVE: Interleave the regions by the weighted interleave ratio
>    * @DAMOS_STAT:		Do nothing but count the stat.
>    * @NR_DAMOS_ACTIONS:	Total number of DAMOS actions
>    *
> @@ -136,6 +137,7 @@ enum damos_action {
>   	DAMOS_LRU_DEPRIO,
>   	DAMOS_MIGRATE_HOT,
>   	DAMOS_MIGRATE_COLD,
> +	DAMOS_INTERLEAVE,
>   	DAMOS_STAT,		/* Do nothing but only record the stat */
>   	NR_DAMOS_ACTIONS,
>   };
> diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
> index 4102a8c5f992..e989464635cd 100644
> --- a/mm/damon/paddr.c
> +++ b/mm/damon/paddr.c
> @@ -535,6 +535,114 @@ static unsigned long damon_pa_migrate(struct damon_region *r, struct damos *s,
>   	return applied * PAGE_SIZE;
>   }
>   
> +#if defined(CONFIG_MEMCG) && defined(CONFIG_NUMA)
> +struct damos_interleave_private {
> +	struct list_head *folio_migration_list;
> +	bool putback_lru;
> +};
> +
> +static bool damon_pa_interleave_rmap(struct folio *folio, struct vm_area_struct *vma,
> +		unsigned long addr, void *arg)
> +{
> +	struct mempolicy *pol;
> +	struct task_struct *task;
> +	pgoff_t ilx;
> +	int target_nid;
> +	struct damos_interleave_private *priv = arg;
> +
> +	task = rcu_dereference(vma->vm_mm->owner);
> +	if (!task)
> +		return true;
> +
> +	pol = get_task_policy(task);
> +	if (!pol)
> +		return true;

Why is this not using get_vma_policy(), which will fallback to the task 
policy in case there is no per-vma policy>

--
Cheers,

David / dhildenb