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Date:   Wed, 2 Nov 2022 08:39:24 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Zach O'Keefe <zokeefe@google.com>
Cc:     Yang Shi <shy828301@gmail.com>, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: don't warn if the node is offlined
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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):

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