+ mm-hugetlb-account-migration-target-folio-in-per-node-nr_hugetlb-vmstat.patch added to mm-unstable branch

+ mm-hugetlb-account-migration-target-folio-in-per-node-nr_hugetlb-vmstat.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/hugetlb: account migration target folio in per-node NR_HUGETLB vmstat
has been added to the -mm mm-unstable branch.  Its filename is
     mm-hugetlb-account-migration-target-folio-in-per-node-nr_hugetlb-vmstat.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-account-migration-target-folio-in-per-node-nr_hugetlb-vmstat.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days

------------------------------------------------------
From: Hongfu Li <lihongfu@kylinos.cn>
Subject: mm/hugetlb: account migration target folio in per-node NR_HUGETLB vmstat
Date: Wed, 23 Sep 2026 10:05:15 +0800

Patch series "mm: fix hugetlb NR_HUGETLB accounting on folio migration", v2.

The hugeTLB counters added by 05d4532b60e3 ("memcg/hugetlb: add hugeTLB
counters to memcg") are maintained in two per-node places:
  - the per-node vmstat counter NR_HUGETLB, exposed as nr_hugetlb in
    /proc/vmstat;
  - the per-node memcg lruvec stat, exposed via memory.numa_stat.

Both are accounted against the folio's node, and both drift when a hugetlb
folio is migrated, though in different ways.

A migration target folio is allocated by alloc_hugetlb_folio_nodemask()
and inherits the old folio's state without ever being accounted, while the
old folio is freed right after and its free is accounted.  That alone
loses vmstat accounting: the target node has no matching increment for the
decrement on the old node, so /proc/vmstat's nr_hugetlb shrinks by
nr_pages per migration.  Patch 1 accounts the folio where it is obtained,
so the increment pairs with the free in free_huge_folio() on the
successful as well as the failed migration path.  The memfd page cache
preallocation helper has the same asymmetry and is fixed in the same
patch.

The per-node lruvec stat breaks differently.  mem_cgroup_migrate() moves
the charge to the new folio and drops the old folio's memcg data, so the
old folio's free right after migration skips the memcg per-node decrement;
the count stays attributed to the old node for the rest of the charge's
life, and the target folio never gets an increment on its new node.  Patch
2 moves that per-node accounting along with the charge, in
move_hugetlb_state().


This patch (of 2):

The NR_HUGETLB vmstat counter is maintained per folio's node: incremented
when a huge page is handed to a user via hugetlb_alloc_folio() and
decremented when it is returned to the pool via free_huge_folio().

A folio obtained by alloc_hugetlb_folio_nodemask() never goes through
hugetlb_alloc_folio(), so it is never accounted, while its free always is.
For a migration target this means the target node gets no matching
increment for the decrement on the old node, so the global nr_hugetlb in
/proc/vmstat drops by nr_pages for each migration.  The same asymmetry
affects the failed migration path, which frees the target again right
away, and the temporary folio hugetlb_mfill_atomic_pte() takes from the
same helper.

alloc_hugetlb_folio_reserve(), used to preallocate the memfd page cache
folios, has the same asymmetry: the folio is handed to a user without
being accounted, while its free is accounted through free_huge_folio().

Account the folio where it is obtained, in alloc_hugetlb_folio_nodemask()
and alloc_hugetlb_folio_reserve(), so that the increment pairs with the
decrement in free_huge_folio(): a successful migration hands the folio to
a user, a failed one frees it again.

Link: https://lore.kernel.org/20260923-for-hugetlb_state3-v2-0-e8a36245bfab@kylinos.cn
Link: https://lore.kernel.org/20260923-for-hugetlb_state3-v2-1-e8a36245bfab@kylinos.cn
Fixes: 05d4532b60e3 ("memcg/hugetlb: add hugeTLB counters to memcg")
Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Acked-by: Muchun Song <muchun.song@linux.dev>
Acked-by: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@kernel.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Chris Down <chris@chrisdown.name>
Cc: <stable@vger.kernel.org>
---

 mm/hugetlb.c |   35 +++++++++++++++++++++++------------
 1 file changed, 23 insertions(+), 12 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlb-account-migration-target-folio-in-per-node-nr_hugetlb-vmstat
+++ a/mm/hugetlb.c
@@ -2206,6 +2206,11 @@ struct folio *alloc_hugetlb_folio_reserv
 	}
 
 	spin_unlock_irq(&hugetlb_lock);
+
+	if (folio)
+		lruvec_stat_mod_folio(folio, NR_HUGETLB,
+				      folio_nr_pages(folio));
+
 	return folio;
 }
 
@@ -2213,24 +2218,30 @@ struct folio *alloc_hugetlb_folio_reserv
 struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid,
 		nodemask_t *nmask, gfp_t gfp_mask, bool allow_alloc_fallback)
 {
-	spin_lock_irq(&hugetlb_lock);
-	if (available_huge_pages(h)) {
-		struct folio *folio;
+	struct folio *folio = NULL;
 
+	spin_lock_irq(&hugetlb_lock);
+	if (available_huge_pages(h))
 		folio = dequeue_hugetlb_folio_nodemask(h, gfp_mask,
 						preferred_nid, nmask);
-		if (folio) {
-			spin_unlock_irq(&hugetlb_lock);
-			return folio;
-		}
-	}
 	spin_unlock_irq(&hugetlb_lock);
 
-	/* We cannot fallback to other nodes, as we could break the per-node pool. */
-	if (!allow_alloc_fallback)
-		gfp_mask |= __GFP_THISNODE;
+	if (!folio) {
+		/*
+		 * We cannot fallback to other nodes, as we could break the
+		 * per-node pool.
+		 */
+		if (!allow_alloc_fallback)
+			gfp_mask |= __GFP_THISNODE;
 
-	return alloc_migrate_hugetlb_folio(h, gfp_mask, preferred_nid, nmask);
+		folio = alloc_migrate_hugetlb_folio(h, gfp_mask, preferred_nid,
+						    nmask);
+	}
+
+	if (folio)
+		lruvec_stat_mod_folio(folio, NR_HUGETLB, folio_nr_pages(folio));
+
+	return folio;
 }
 
 static nodemask_t *policy_mbind_nodemask(gfp_t gfp)
_

Patches currently in -mm which might be from lihongfu@kylinos.cn are

mm-use-a-folio-in-the-softleaf_is_device_private-path.patch
mm-hugetlb-fix-resv_huge_pages-double-decrement-in-memfd-error-path.patch
mm-memcontrol-remove-unused-memcg-parameter-in-calculate_high_delay.patch
selftests-mm-khugepaged-consolidate-error-exits-via-kselftest-helpers.patch
mm-page_owner-preserve-original-free_pid-free_tgid-during-folio-migration.patch
mm-memfd-fix-hugetlb-reservation-accounting-in-error-paths.patch
selftests-mm-fix-ptrace-peekdata-check-in-memfd_secret-test.patch
mm-hugetlb_cgroup-move-per-node-usage-on-cross-node-migration.patch
mm-hugetlb_cgroup-move-per-node-usage-on-cgroup-reparenting.patch
mm-hugetlb-account-migration-target-folio-in-per-node-nr_hugetlb-vmstat.patch
mm-memcg-migrate-per-node-hugetlb-lruvec-stat-together-with-hugetlb-folio.patch