Re: [External] [PATCH v2 2/5] hugetlb: convert page_huge_active() HPageMigratable flag

Muchun Song
2021-02-03T07:44:22Z

On Wed, Jan 20, 2021 at 9:33 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> 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 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.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

Hi Mike,

I found that you may forget to remove set_page_huge_active()
from include/linux/hugetlb.h.

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 37fd248ce271..6f680cf0eee6 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -852,7 +852,7 @@ static inline void
huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
}
#endif

-void set_page_huge_active(struct page *page);
+

Thanks.