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authorMike Kravetz <mike.kravetz@oracle.com>2021-02-24 23:08:56 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-02-25 00:38:34 +0300
commit8f251a3d5ce3bdea73bd045ed35db64f32e0d0d9 (patch)
treeba7424cb761d8e03cfa1ebc047a450a4619004fc /mm/memory_hotplug.c
parentd6995da311221a05c8aef3bda2629e5cb14c7302 (diff)
downloadlinux-8f251a3d5ce3bdea73bd045ed35db64f32e0d0d9.tar.xz
hugetlb: convert page_huge_active() HPageMigratable flag
Use the new hugetlb page specific flag HPageMigratable to replace the page_huge_active interfaces. By it's name, page_huge_active implied that a huge page was on the active list. However, that is not really what code checking the flag wanted to know. It really wanted to determine if the huge page could be migrated. This happens when the page is actually added to the page cache and/or task page table. This is the reasoning behind the name change. The VM_BUG_ON_PAGE() calls in the *_huge_active() interfaces are not really necessary as we KNOW the page is a hugetlb page. Therefore, they are removed. The routine page_huge_active checked for PageHeadHuge before testing the active bit. This is unnecessary in the case where we hold a reference or lock and know it is a hugetlb head page. page_huge_active is also called without holding a reference or lock (scan_movable_pages), and can race with code freeing the page. The extra check in page_huge_active shortened the race window, but did not prevent the race. Offline code calling scan_movable_pages already deals with these races, so removing the check is acceptable. Add comment to racy code. [songmuchun@bytedance.com: remove set_page_huge_active() declaration from include/linux/hugetlb.h] Link: https://lkml.kernel.org/r/CAMZfGtUda+KoAZscU0718TN61cSFwp4zy=y2oZ=+6Z2TAZZwng@mail.gmail.com Link: https://lkml.kernel.org/r/20210122195231.324857-3-mike.kravetz@oracle.com Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> Reviewed-by: Oscar Salvador <osalvador@suse.de> Reviewed-by: Muchun Song <songmuchun@bytedance.com> Reviewed-by: Miaohe Lin <linmiaohe@huawei.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: David Hildenbrand <david@redhat.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memory_hotplug.c')
-rw-r--r--mm/memory_hotplug.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index ddcb1cd24c60..abe43c1ae920 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1260,7 +1260,14 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
if (!PageHuge(page))
continue;
head = compound_head(page);
- if (page_huge_active(head))
+ /*
+ * This test is racy as we hold no reference or lock. The
+ * hugetlb page could have been free'ed and head is no longer
+ * a hugetlb page before the following check. In such unlikely
+ * cases false positives and negatives are possible. Calling
+ * code must deal with these scenarios.
+ */
+ if (HPageMigratable(head))
goto found;
skip = compound_nr(head) - (page - head);
pfn += skip - 1;