+ mmhugetlb-use-folio-fields-in-second-tail-page-fix.patch added to mm-unstable branch

+ mmhugetlb-use-folio-fields-in-second-tail-page-fix.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm,hugetlb: use folio fields in second tail page: fix
has been added to the -mm mm-unstable branch.  Its filename is
     mmhugetlb-use-folio-fields-in-second-tail-page-fix.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mmhugetlb-use-folio-fields-in-second-tail-page-fix.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Hugh Dickins <hughd@google.com>
Subject: mm,hugetlb: use folio fields in second tail page: fix
Date: Wed, 9 Nov 2022 18:13:50 -0800 (PST)

Per review comment from Sidhartha: prefix folio's page_1 and page_2 with
double underscore, to underscore that they are fillers for alignment
rather than directly usable members of the union (whereas the first
"struct page page" is important for folio<->page conversions).

Per review comment from Kirill: give folio's _flags_2 and _head_2 a line
of documentation each, though both of them "Do not use" (I think _flags_1
should be enough for now, and shouldn't recommend spilling to _flags_2).

Link: https://lkml.kernel.org/r/9e2cb6b-5b58-d3f2-b5ee-5f8a14e8f10@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: James Houghton <jthoughton@google.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zach O'Keefe <zokeefe@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm_types.h |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/include/linux/mm_types.h~mmhugetlb-use-folio-fields-in-second-tail-page-fix
+++ a/include/linux/mm_types.h
@@ -273,6 +273,8 @@ struct page {
  * @_total_mapcount: Do not use directly, call folio_entire_mapcount().
  * @_pincount: Do not use directly, call folio_maybe_dma_pinned().
  * @_folio_nr_pages: Do not use directly, call folio_nr_pages().
+ * @_flags_2: For alignment.  Do not use.
+ * @_head_2: Points to the folio.  Do not use.
  * @_hugetlb_subpool: Do not use directly, use accessor in hugetlb.h.
  * @_hugetlb_cgroup: Do not use directly, use accessor in hugetlb_cgroup.h.
  * @_hugetlb_cgroup_rsvd: Do not use directly, use accessor in hugetlb_cgroup.h.
@@ -327,7 +329,7 @@ struct folio {
 			unsigned int _folio_nr_pages;
 #endif
 		};
-		struct page page_1;
+		struct page __page_1;
 	};
 	union {
 		struct {
@@ -338,7 +340,7 @@ struct folio {
 			void *_hugetlb_cgroup_rsvd;
 			void *_hugetlb_hwpoison;
 		};
-		struct page page_2;
+		struct page __page_2;
 	};
 };
 
_

Patches currently in -mm which might be from hughd@google.com are

mmhugetlb-use-folio-fields-in-second-tail-page.patch
mmhugetlb-use-folio-fields-in-second-tail-page-fix.patch
mmthprmap-simplify-compound-page-mapcount-handling.patch
mmthprmap-lock_compound_mapcounts-on-thp-mapcounts.patch