linux-kernel - Re: [PATCH] mm: don't warn if the node is offlined

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Date:   Wed, 2 Nov 2022 09:03:57 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     "Zach O'Keefe" <zokeefe@...gle.com>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: don't warn if the node is offlined

On Wed, Nov 2, 2022 at 12:39 AM Michal Hocko <mhocko@...e.com> wrote:
>
> On Tue 01-11-22 12:13:35, Zach O'Keefe wrote:
> [...]
> > This is slightly tangential - but I don't want to send a new mail
> > about it -- but I wonder if we should be doing __GFP_THISNODE +
> > explicit node vs having hpage_collapse_find_target_node() set a
> > nodemask. We could then provide fallback nodes for ties, or if some
> > node contained > some threshold number of pages.
>
> I would simply go with something like this (not even compile tested):

Thanks, Michal. It is definitely an option. As I talked with Zach, I'm
not sure whether it is worth making the code more complicated for such
micro optimization or not. Removing __GFP_THISNODE or even removing
the node balance code should be fine too IMHO. TBH I doubt there would
be any noticeable difference.

>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 4734315f7940..947a5158fe11 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -96,9 +96,6 @@ struct collapse_control {
>
>         /* Num pages scanned per node */
>         u32 node_load[MAX_NUMNODES];
> -
> -       /* Last target selected in hpage_collapse_find_target_node() */
> -       int last_target_node;
>  };
>
>  /**
> @@ -734,7 +731,6 @@ static void khugepaged_alloc_sleep(void)
>
>  struct collapse_control khugepaged_collapse_control = {
>         .is_khugepaged = true,
> -       .last_target_node = NUMA_NO_NODE,
>  };
>
>  static bool hpage_collapse_scan_abort(int nid, struct collapse_control *cc)
> @@ -772,7 +768,7 @@ static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
>  }
>
>  #ifdef CONFIG_NUMA
> -static int hpage_collapse_find_target_node(struct collapse_control *cc)
> +static int hpage_collapse_find_target_node(struct collapse_control *cc, nodemask_t *alloc_mask)
>  {
>         int nid, target_node = 0, max_value = 0;
>
> @@ -783,28 +779,25 @@ static int hpage_collapse_find_target_node(struct collapse_control *cc)
>                         target_node = nid;
>                 }
>
> +       nodes_clear(&alloc_mask);
>         /* do some balance if several nodes have the same hit record */
> -       if (target_node <= cc->last_target_node)
> -               for (nid = cc->last_target_node + 1; nid < MAX_NUMNODES;
> -                    nid++)
> -                       if (max_value == cc->node_load[nid]) {
> -                               target_node = nid;
> -                               break;
> -                       }
> +       for_each_online_node(nid) {_
> +               if (max_value == cc->node_load[nid])
> +                       node_set(nid, &alloc_mask)
> +       }
>
> -       cc->last_target_node = target_node;
>         return target_node;
>  }
>  #else
> -static int hpage_collapse_find_target_node(struct collapse_control *cc)
> +static int hpage_collapse_find_target_node(struct collapse_control *cc, nodemask_t *alloc_mask)
>  {
>         return 0;
>  }
>  #endif
>
> -static bool hpage_collapse_alloc_page(struct page **hpage, gfp_t gfp, int node)
> +static bool hpage_collapse_alloc_page(struct page **hpage, gfp_t gfp, int node, nodemask_t *nmask)
>  {
> -       *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
> +       *hpage = __alloc_pages(gfp, HPAGE_PMD_ORDER, node, nmask);
>         if (unlikely(!*hpage)) {
>                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
>                 return false;
> @@ -958,9 +951,18 @@ static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
>         /* Only allocate from the target node */
>         gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
>                      GFP_TRANSHUGE) | __GFP_THISNODE;
> -       int node = hpage_collapse_find_target_node(cc);
> +       NODEMASK_ALLOC(nodemask_t, nmask, GFP_KERNEL);
> +       int node;
> +       int ret;
> +
> +       if (!nmaks)
> +               return SCAN_ALLOC_HUGE_PAGE_FAIL;
> +
> +       node = hpage_collapse_find_target_node(cc, nmask);
> +       ret = hpage_collapse_alloc_page(hpage, gfp, node, nmask);
> +       NODEMASK_FREE(nmask);
>
> -       if (!hpage_collapse_alloc_page(hpage, gfp, node))
> +       if (!ret)
>                 return SCAN_ALLOC_HUGE_PAGE_FAIL;
>         if (unlikely(mem_cgroup_charge(page_folio(*hpage), mm, gfp)))
>                 return SCAN_CGROUP_CHARGE_FAIL;
> @@ -2576,7 +2578,6 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
>         if (!cc)
>                 return -ENOMEM;
>         cc->is_khugepaged = false;
> -       cc->last_target_node = NUMA_NO_NODE;
>
>         mmgrab(mm);
>         lru_add_drain_all();
> --
> Michal Hocko
> SUSE Labs