+ mm-migrate-do-not-migrate-hugetlb-page-whose-refcount-is-one.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: mm: migrate: do not migrate HugeTLB page whose refcount is one
has been added to the -mm tree.  Its filename is
     mm-migrate-do-not-migrate-hugetlb-page-whose-refcount-is-one.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-migrate-do-not-migrate-hugetlb-page-whose-refcount-is-one.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-migrate-do-not-migrate-hugetlb-page-whose-refcount-is-one.patch

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------------------------------------------------------
From: Muchun Song <songmuchun@bytedance.com>
Subject: mm: migrate: do not migrate HugeTLB page whose refcount is one

If the refcount is one when it is migrated, it means that the page
was freed from under us. So we are done and do not need to migrate.

This optimization is consistent with the regular pages, just like
unmap_and_move() does.

Link: https://lkml.kernel.org/r/20210110124017.86750-2-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: Yang Shi <shy828301@gmail.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/migrate.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/mm/migrate.c~mm-migrate-do-not-migrate-hugetlb-page-whose-refcount-is-one
+++ a/mm/migrate.c
@@ -1284,6 +1284,12 @@ static int unmap_and_move_huge_page(new_
 		return -ENOSYS;
 	}
 
+	if (page_count(hpage) == 1) {
+		/* page was freed from under us. So we are done. */
+		putback_active_hugepage(hpage);
+		return MIGRATEPAGE_SUCCESS;
+	}
+
 	new_hpage = get_new_page(hpage, private);
 	if (!new_hpage)
 		return -ENOMEM;
_

Patches currently in -mm which might be from songmuchun@bytedance.com are

mm-hugetlbfs-fix-cannot-migrate-the-fallocated-hugetlb-page.patch
mm-hugetlb-fix-a-race-between-freeing-and-dissolving-the-page.patch
mm-hugetlb-fix-a-race-between-isolating-and-freeing-page.patch
mm-hugetlb-remove-vm_bug_on_page-from-page_huge_active.patch
mm-memcontrol-optimize-per-lruvec-stats-counter-memory-usage.patch
mm-memcontrol-fix-nr_anon_thps-accounting-in-charge-moving.patch
mm-memcontrol-convert-nr_anon_thps-account-to-pages.patch
mm-memcontrol-convert-nr_file_thps-account-to-pages.patch
mm-memcontrol-convert-nr_shmem_thps-account-to-pages.patch
mm-memcontrol-convert-nr_shmem_pmdmapped-account-to-pages.patch
mm-memcontrol-convert-nr_file_pmdmapped-account-to-pages.patch
mm-memcontrol-make-the-slab-calculation-consistent.patch
mm-migrate-do-not-migrate-hugetlb-page-whose-refcount-is-one.patch
mm-hugetlb-add-return-eagain-for-dissolve_free_huge_page.patch