Re: [RFC PATCH] mm: add last level page table numa info to /proc/pid/numa_pgtable

[Matthew Wilcox <willy@infradead.org>]

On Sun, Jul 31, 2022 at 12:35:28AM +0800, Xin Hao wrote:
> In many data center servers, the shared memory architectures is
> Non-Uniform Memory Access (NUMA), remote numa node data access
> often brings a high latency problem, but what we are easy to ignore
> is that the page table remote numa access, It can also leads to a
> performance degradation.
> 
> So there add a new interface in /proc, This will help developers to
> get more info about performance issues if they are caused by cross-NUMA.

Interesting.  The implementation seems rather more complex than
necessary though.

> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 2d04e3470d4c..a51befb47ea8 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1999,4 +1999,133 @@ const struct file_operations proc_pid_numa_maps_operations = {
>  	.release	= proc_map_release,
>  };
> 
> +struct pgtable_numa_maps {
> +	unsigned long node[MAX_NUMNODES];
> +};
> +
> +struct pgtable_numa_private {
> +	struct proc_maps_private proc_maps;
> +	struct pgtable_numa_maps md;
> +};

struct pgtable_numa_private {
	struct proc_maps_private proc_maps;
	unsigned long node[MAX_NUMNODES];
};

> +static void gather_pgtable_stats(struct page *page, struct pgtable_numa_maps *md)
> +{
> +	md->node[page_to_nid(page)] += 1;
> +}
> +
> +static struct page *can_gather_pgtable_numa_stats(pmd_t pmd, struct vm_area_struct *vma,
> +		unsigned long addr)
> +{
> +	struct page *page;
> +	int nid;
> +
> +	if (!pmd_present(pmd))
> +		return NULL;
> +
> +	if (pmd_huge(pmd))
> +		return NULL;
> +
> +	page = pmd_page(pmd);
> +	nid = page_to_nid(page);
> +	if (!node_isset(nid, node_states[N_MEMORY]))
> +		return NULL;
> +
> +	return page;
> +}
> +
> +static int gather_pgtable_numa_stats(pmd_t *pmd, unsigned long addr,
> +		unsigned long end, struct mm_walk *walk)
> +{
> +	struct pgtable_numa_maps *md = walk->private;
> +	struct vm_area_struct *vma = walk->vma;
> +	struct page *page;
> +
> +	if (pmd_huge(*pmd)) {
> +		struct page *pmd_page;
> +
> +		pmd_page = virt_to_page(pmd);
> +		if (!pmd_page)
> +			return 0;
> +
> +		if (!node_isset(page_to_nid(pmd_page), node_states[N_MEMORY]))
> +			return 0;
> +
> +		gather_pgtable_stats(pmd_page, md);
> +		goto out;
> +	}
> +
> +	page = can_gather_pgtable_numa_stats(*pmd, vma, addr);
> +	if (!page)
> +		return 0;
> +
> +	gather_pgtable_stats(page, md);
> +
> +out:
> +	cond_resched();
> +	return 0;
> +}

static int gather_pgtable_numa_stats(pmd_t *pmd, unsigned long addr,
		unsigned long end, struct mm_walk *walk)
{
	struct pgtable_numa_private *priv = walk->private;
	struct vm_area_struct *vma = walk->vma;
	struct page *page;
	int nid;

	if (pmd_huge(*pmd)) {
		page = virt_to_page(pmd);
	} else {
		page = pmd_page(*pmd);
	}

	nid = page_to_nid(page);
	priv->node[nid]++;

	return 0;
}