+ mm-hugetlb-check-gigantic_page_runtime_supported-in-return_unused_surplus_pages.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/hugetlb: check gigantic_page_runtime_supported() in return_unused_surplus_pages()
has been added to the -mm mm-unstable branch.  Its filename is
     mm-hugetlb-check-gigantic_page_runtime_supported-in-return_unused_surplus_pages.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-check-gigantic_page_runtime_supported-in-return_unused_surplus_pages.patch

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

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------------------------------------------------------
From: Naoya Horiguchi <naoya.horiguchi@nec.com>
Subject: mm/hugetlb: check gigantic_page_runtime_supported() in return_unused_surplus_pages()
Date: Mon, 4 Jul 2022 10:33:04 +0900

Patch series "mm, hwpoison: enable 1GB hugepage support", v4.


This patch (of 9):

I found a weird state of 1GB hugepage pool, caused by the following
procedure:

  - run a process reserving all free 1GB hugepages,
  - shrink free 1GB hugepage pool to zero (i.e. writing 0 to
    /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then
  - kill the reserving process.

, then all the hugepages are free *and* surplus at the same time.

  $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
  3
  $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages
  3
  $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages
  0
  $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages
  3

This state is resolved by reserving and allocating the pages then freeing
them again, so this seems not to result in serious problem.  But it's a
little surprising (shrinking pool suddenly fails).

This behavior is caused by hstate_is_gigantic() check in
return_unused_surplus_pages().  This was introduced so long ago in 2008 by
commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and at
that time the gigantic pages were not supposed to be allocated/freed at
run-time.  Now kernel can support runtime allocation/free, so let's check
gigantic_page_runtime_supported() together.

Link: https://lkml.kernel.org/r/20220704013312.2415700-1-naoya.horiguchi@linux.dev
Link: https://lkml.kernel.org/r/20220704013312.2415700-2-naoya.horiguchi@linux.dev
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Liu Shixin <liushixin2@huawei.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |   19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlb-check-gigantic_page_runtime_supported-in-return_unused_surplus_pages
+++ a/mm/hugetlb.c
@@ -2432,8 +2432,7 @@ static void return_unused_surplus_pages(
 	/* Uncommit the reservation */
 	h->resv_huge_pages -= unused_resv_pages;
 
-	/* Cannot return gigantic pages currently */
-	if (hstate_is_gigantic(h))
+	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		goto out;
 
 	/*
@@ -3313,7 +3312,8 @@ static int set_max_huge_pages(struct hst
 	 * the user tries to allocate gigantic pages but let the user free the
 	 * boottime allocated gigantic pages.
 	 */
-	if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) {
+	if (hstate_is_gigantic(h) && (!IS_ENABLED(CONFIG_CONTIG_ALLOC) ||
+				      !gigantic_page_runtime_supported())) {
 		if (count > persistent_huge_pages(h)) {
 			spin_unlock_irq(&hugetlb_lock);
 			mutex_unlock(&h->resize_lock);
@@ -3362,6 +3362,19 @@ static int set_max_huge_pages(struct hst
 	}
 
 	/*
+	 * We can not decrease gigantic pool size if runtime modification
+	 * is not supported.
+	 */
+	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) {
+		if (count < persistent_huge_pages(h)) {
+			spin_unlock_irq(&hugetlb_lock);
+			mutex_unlock(&h->resize_lock);
+			NODEMASK_FREE(node_alloc_noretry);
+			return -EINVAL;
+		}
+	}
+
+	/*
 	 * Decrease the pool size
 	 * First return free pages to the buddy allocator (being careful
 	 * to keep enough around to satisfy reservations).  Then place
_

Patches currently in -mm which might be from naoya.horiguchi@nec.com are

mm-hugetlb-check-gigantic_page_runtime_supported-in-return_unused_surplus_pages.patch
mm-hugetlb-separate-path-for-hwpoison-entry-in-copy_hugetlb_page_range.patch
mm-hugetlb-make-pud_huge-and-follow_huge_pud-aware-of-non-present-pud-entry.patch
mm-hwpoison-hugetlb-support-saving-mechanism-of-raw-error-pages.patch
mm-hwpoison-make-unpoison-aware-of-raw-error-info-in-hwpoisoned-hugepage.patch
mm-hwpoison-set-pg_hwpoison-for-busy-hugetlb-pages.patch
mm-hwpoison-make-__page_handle_poison-returns-int.patch
mm-hwpoison-skip-raw-hwpoison-page-in-freeing-1gb-hugepage.patch
mm-hwpoison-enable-memory-error-handling-on-1gb-hugepage.patch