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

On Wed, Jan 20, 2021 at 9:33 AM Mike Kravetz [off-list ref] 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 <redacted>

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.