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Message-ID: <0c1f9e76-9b1d-7069-bb09-c18e4f19f0c4@redhat.com>
Date: Mon, 1 Aug 2022 15:28:15 +0200
From: David Hildenbrand <david@...hat.com>
To: Xin Hao <xhao@...ux.alibaba.com>, willy@...radead.org
Cc: akpm@...ux-foundation.org, adobriyan@...il.com,
keescook@...omium.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [RFC PATCH V4 1/1] mm: add last level page table numa info to
/proc/pid/numa_pgtable
On 01.08.22 14:17, 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.
Let me try rewriting:
"
Many data center servers employ Non-Uniform Memory Access (NUMA)
architectures. Remote numa memory access results in high latency. While
memory placement is one issue, sub-optimal page table placement can also
result in surprise 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.
Why do we only care about "last level page table", why not about the others?
IMHO, we could emit something like "0, 1, 3, 0" instead for a given user
space address, showing the NUMA node the page table belongs to from
highest to lowest page table level.
>
> Reported-by: kernel test robot <lkp@...el.com>
The kernel test robot reported that we need "/proc/pid/numa_pgtable" ?! :)
Just drop that unless it's a follow-up fix.
> Signed-off-by: Xin Hao <xhao@...ux.alibaba.com>
> ---
> fs/proc/base.c | 2 ++
> fs/proc/internal.h | 1 +
> fs/proc/task_mmu.c | 87 ++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 90 insertions(+)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 8dfa36a99c74..487e82dd3275 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -3224,6 +3224,7 @@ static const struct pid_entry tgid_base_stuff[] = {
> REG("maps", S_IRUGO, proc_pid_maps_operations),
> #ifdef CONFIG_NUMA
> REG("numa_maps", S_IRUGO, proc_pid_numa_maps_operations),
> + REG("numa_pgtable", S_IRUGO, proc_pid_numa_pgtable_operations),
> #endif
> REG("mem", S_IRUSR|S_IWUSR, proc_mem_operations),
> LNK("cwd", proc_cwd_link),
> @@ -3571,6 +3572,7 @@ static const struct pid_entry tid_base_stuff[] = {
> #endif
> #ifdef CONFIG_NUMA
> REG("numa_maps", S_IRUGO, proc_pid_numa_maps_operations),
> + REG("numa_pgtable", S_IRUGO, proc_pid_numa_pgtable_operations),
> #endif
> REG("mem", S_IRUSR|S_IWUSR, proc_mem_operations),
> LNK("cwd", proc_cwd_link),
> diff --git a/fs/proc/internal.h b/fs/proc/internal.h
> index 06a80f78433d..e7ed9ef097b6 100644
> --- a/fs/proc/internal.h
> +++ b/fs/proc/internal.h
> @@ -296,6 +296,7 @@ struct mm_struct *proc_mem_open(struct inode *inode, unsigned int mode);
>
> extern const struct file_operations proc_pid_maps_operations;
> extern const struct file_operations proc_pid_numa_maps_operations;
> +extern const struct file_operations proc_pid_numa_pgtable_operations;
> extern const struct file_operations proc_pid_smaps_operations;
> extern const struct file_operations proc_pid_smaps_rollup_operations;
> extern const struct file_operations proc_clear_refs_operations;
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 2d04e3470d4c..77b7a49757f5 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1999,4 +1999,91 @@ const struct file_operations proc_pid_numa_maps_operations = {
> .release = proc_map_release,
> };
>
> +struct pgtable_numa_private {
> + struct proc_maps_private proc_maps;
> + unsigned long node[MAX_NUMNODES];
> +};
> +
> +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 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;
> +}
> +
> +static const struct mm_walk_ops show_numa_pgtable_ops = {
> + .pmd_entry = gather_pgtable_numa_stats,
> +};
> +
> +/*
> + * Display the page talbe allocated per node via /proc.
s/talbe/table/
but the comment somehow doesn't make sense. We don't display a page table.
> + */
> +static int show_numa_pgtable(struct seq_file *m, void *v)
> +{
> + struct pgtable_numa_private *numa_priv = m->private;
> + struct vm_area_struct *vma = v;
> + struct mm_struct *mm = vma->vm_mm;
> + struct file *file = vma->vm_file;
> + int nid;
> +
> + if (!mm)
> + return 0;
> +
> + memset(numa_priv->node, 0, sizeof(numa_priv->node));
> +
> + seq_printf(m, "%08lx ", vma->vm_start);
> +
> + if (file) {
> + seq_puts(m, " file=");
> + seq_file_path(m, file, "\n\t= ");
> + } else if (vma->vm_start <= mm->brk && vma->vm_end >= mm->start_brk) {
> + seq_puts(m, " heap");
> + } else if (is_stack(vma)) {
> + seq_puts(m, " stack");
> + }
> +
> + /* mmap_lock is held by m_start */
> + walk_page_vma(vma, &show_numa_pgtable_ops, numa_priv);
> +
> + for_each_node_state(nid, N_MEMORY) {
> + if (numa_priv->node[nid])
> + seq_printf(m, " N%d=%lu", nid, numa_priv->node[nid]);
> + }
> + seq_putc(m, '\n');
> +
> + return 0;
> +}
> +
> +static const struct seq_operations proc_pid_numa_pgtable_op = {
> + .start = m_start,
> + .next = m_next,
> + .stop = m_stop,
> + .show = show_numa_pgtable,
> +};
> +
> +static int pid_numa_pgtable_open(struct inode *inode, struct file *file)
> +{
> + return proc_maps_open(inode, file, &proc_pid_numa_pgtable_op,
> + sizeof(struct pgtable_numa_private));
> +}
> +
> +const struct file_operations proc_pid_numa_pgtable_operations = {
> + .open = pid_numa_pgtable_open,
> + .read = seq_read,
> + .llseek = seq_lseek,
> + .release = proc_map_release,
> +};
> +
> #endif /* CONFIG_NUMA */
> --
> 2.31.0
>
--
Thanks,
David / dhildenb
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