Re: [RFC V3 PATCH] mm: add last level page table numa info to /proc/pid/numa_pgtable

[haoxin <xhao@xxxxxxxxxxxxxxxxx>]

在 2022/8/1 下午2:06, Baolin Wang 写道:
> Hi Xin,
>
> On 8/1/2022 11:27 AM, 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.
> >
> > V2 -> V3
> > 1, Fix compile warning bug.
> >
> > V1 -> V2
> > 1, As Matthew Wilcox advise, Simplify the code.
> > 2, Do some codes format fix.
>
> Please move the changes history under your 'Signed-off-by' with '---'.
>
> > V2: 
> > https://lore.kernel.org/linux-mm/20220731155223.60238-1-xhao@xxxxxxxxxxxxxxxxx/
> > V1: 
> > https://lore.kernel.org/linux-mm/YuVqdcY8Ibib2LJa@xxxxxxxxxxxxxxxxxxxx/T/
> >
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > Signed-off-by: Xin Hao <xhao@xxxxxxxxxxxxxxxxx>
> > ---
> >   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);
>
> You should validate if the pmd is valid or present before getting the 
> pagetable page.
>
> if (pmd_none(*pmd) || !pmd_present(*pmd))
>
> Another issue is I think you should hold the pmd lock to call 
> pmd_page(), since after the validation of pmd_huge(), the pmd entry 
> can be modified by other threads if you did not hold the pmd lock.
Thanks, Baolin, i will fix it in the next version.
> > +    }
> > +
> > +    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.
> > + */
> > +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