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hugetlb: convert page_huge_active() HPageMigratable flag

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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>
This commit is contained in:
Mike Kravetz
2021-02-24 12:08:56 -08:00
committed by Linus Torvalds
parent d6995da311
commit 8f251a3d5c
5 changed files with 25 additions and 44 deletions
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6
include/linux/page-flags.h
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@@ -592,15 +592,9 @@ static inline void ClearPageCompound(struct page *page)
#ifdef CONFIG_HUGETLB_PAGE
int PageHuge(struct page *page);
int PageHeadHuge(struct page *page);
bool page_huge_active(struct page *page);
#else
TESTPAGEFLAG_FALSE(Huge)
TESTPAGEFLAG_FALSE(HeadHuge)
static inline bool page_huge_active(struct page *page)
{
return 0;
}
#endif