Re: [PATCH v4 3/7] padata: dispatch works on different nodes

[Muchun Song <muchun.song@linux.dev>]

On 2024/1/18 20:39, Gang Li wrote:
> When a group of tasks that access different nodes are scheduled on the
> same node, they may encounter bandwidth bottlenecks and access latency.
>
> Thus, numa_aware flag is introduced here, allowing tasks to be
> distributed across different nodes to fully utilize the advantage of
> multi-node systems.
>
> Signed-off-by: Gang Li <gang.li@linux.dev>
> Tested-by: David Rientjes <rientjes@google.com>
> ---
>   include/linux/padata.h |  3 +++
>   kernel/padata.c        | 14 ++++++++++++--
>   mm/mm_init.c           |  1 +
>   3 files changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/padata.h b/include/linux/padata.h
> index 495b16b6b4d7..f79ccd50e7f4 100644
> --- a/include/linux/padata.h
> +++ b/include/linux/padata.h
> @@ -137,6 +137,8 @@ struct padata_shell {
>    *             appropriate for one worker thread to do at once.
>    * @max_threads: Max threads to use for the job, actual number may be less
>    *               depending on task size and minimum chunk size.
> + * @numa_aware: Dispatch jobs to different nodes. If a node only has memory but
> + *              no CPU, dispatch its jobs to a random CPU.
>    */
>   struct padata_mt_job {
>   	void (*thread_fn)(unsigned long start, unsigned long end, void *arg);
> @@ -146,6 +148,7 @@ struct padata_mt_job {
>   	unsigned long		align;
>   	unsigned long		min_chunk;
>   	int			max_threads;
> +	bool			numa_aware;
>   };
>   
>   /**
> diff --git a/kernel/padata.c b/kernel/padata.c
> index 179fb1518070..10eae3f59203 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -485,7 +485,8 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>   	struct padata_work my_work, *pw;
>   	struct padata_mt_job_state ps;
>   	LIST_HEAD(works);
> -	int nworks;
> +	int nworks, nid;
> +	static atomic_t last_used_nid = ATOMIC_INIT(0);
last_used_nid is only used during boot time so it could be
__init_data. Otherwise, LGTM.

Reviewed-by: Muchun Song <muchun.song@linux.dev>

>   
>   	if (job->size == 0)
>   		return;
> @@ -517,7 +518,16 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>   	ps.chunk_size = roundup(ps.chunk_size, job->align);
>   
>   	list_for_each_entry(pw, &works, pw_list)
> -		queue_work(system_unbound_wq, &pw->pw_work);
> +		if (job->numa_aware) {
> +			int old_node = atomic_read(&last_used_nid);
> +
> +			do {
> +				nid = next_node_in(old_node, node_states[N_CPU]);
> +			} while (!atomic_try_cmpxchg(&last_used_nid, &old_node, nid));
> +			queue_work_node(nid, system_unbound_wq, &pw->pw_work);
> +		} else {
> +			queue_work(system_unbound_wq, &pw->pw_work);
> +		}
>   
>   	/* Use the current thread, which saves starting a workqueue worker. */
>   	padata_work_init(&my_work, padata_mt_helper, &ps, PADATA_WORK_ONSTACK);
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 2c19f5515e36..549e76af8f82 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -2231,6 +2231,7 @@ static int __init deferred_init_memmap(void *data)
>   			.align       = PAGES_PER_SECTION,
>   			.min_chunk   = PAGES_PER_SECTION,
>   			.max_threads = max_threads,
> +			.numa_aware  = false,
>   		};
>   
>   		padata_do_multithreaded(&job);