mm,hugetlb: use folio fields in second tail page

Patch series "mm,huge,rmap: unify and speed up compound mapcounts".


This patch (of 3):

We want to declare one more int in the first tail of a compound page: that
first tail page being valuable property, since every compound page has a
first tail, but perhaps no more than that.

No problem on 64-bit: there is already space for it.  No problem with
32-bit THPs: 5.18 commit 5232c63f46fd ("mm: Make compound_pincount always
available") kindly cleared the space for it, apparently not realizing that
only 64-bit architectures enable CONFIG_THP_SWAP (whose use of tail
page->private might conflict) - but make sure of that in its Kconfig.

But hugetlb pages use tail page->private of the first tail page for a
subpool pointer, which will conflict; and they also use page->private of
the 2nd, 3rd and 4th tails.

Undo "mm: add private field of first tail to struct page and struct
folio"'s recent addition of private_1 to the folio tail: instead add
hugetlb_subpool, hugetlb_cgroup, hugetlb_cgroup_rsvd, hugetlb_hwpoison to
a second tail page of the folio: THP has long been using several fields of
that tail, so make better use of it for hugetlb too.  This is not how a
generic folio should be declared in future, but it is an effective
transitional way to make use of it.

Delete the SUBPAGE_INDEX stuff, but keep __NR_USED_SUBPAGE: now 3.

[hughd@google.com: prefix folio's page_1 and page_2 with double underscore,
  give folio's _flags_2 and _head_2 a line documentation each]
  Link: https://lkml.kernel.org/r/9e2cb6b-5b58-d3f2-b5ee-5f8a14e8f10@google.com
Link: https://lkml.kernel.org/r/5f52de70-975-e94f-f141-543765736181@google.com
Link: https://lkml.kernel.org/r/3818cc9a-9999-d064-d778-9c94c5911e6@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: James Houghton <jthoughton@google.com>
Cc: John Hubbard <jhubbard@nvidia.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>

2 files changed, 3 insertions, 4 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index 4b28800d9be1..c86b69aff7d4 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -775,7 +775,7 @@ endchoice
 
 config THP_SWAP
 	def_bool y
-	depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_SWAP && SWAP
+	depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_SWAP && SWAP && 64BIT
 	help
 	  Swap transparent huge pages in one piece, without splitting.
 	  XXX: For now, swap cluster backing transparent huge page
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 779a426d2cab..63d8501001c6 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1687,8 +1687,7 @@ EXPORT_SYMBOL_GPL(mf_dax_kill_procs);
 #ifdef CONFIG_HUGETLB_PAGE
 /*
  * Struct raw_hwp_page represents information about "raw error page",
- * constructing singly linked list originated from ->private field of
- * SUBPAGE_INDEX_HWPOISON-th tail page.
+ * constructing singly linked list from ->_hugetlb_hwpoison field of folio.
  */
 struct raw_hwp_page {
 	struct llist_node node;
@@ -1697,7 +1696,7 @@ struct raw_hwp_page {
 
 static inline struct llist_head *raw_hwp_list_head(struct page *hpage)
 {
-	return (struct llist_head *)&page_private(hpage + SUBPAGE_INDEX_HWPOISON);
+	return (struct llist_head *)&page_folio(hpage)->_hugetlb_hwpoison;
 }
 
 static unsigned long __free_raw_hwp_pages(struct page *hpage, bool move_flag)