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>

1 files changed, 5 insertions, 18 deletions

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 58a30938a9b1..551834cd5299 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -33,22 +33,9 @@ typedef struct { unsigned long pd; } hugepd_t;
 /*
  * For HugeTLB page, there are more metadata to save in the struct page. But
  * the head struct page cannot meet our needs, so we have to abuse other tail
- * struct page to store the metadata. In order to avoid conflicts caused by
- * subsequent use of more tail struct pages, we gather these discrete indexes
- * of tail struct page here.
+ * struct page to store the metadata.
  */
-enum {
-	SUBPAGE_INDEX_SUBPOOL = 1,	/* reuse page->private */
-#ifdef CONFIG_CGROUP_HUGETLB
-	SUBPAGE_INDEX_CGROUP,		/* reuse page->private */
-	SUBPAGE_INDEX_CGROUP_RSVD,	/* reuse page->private */
-	__MAX_CGROUP_SUBPAGE_INDEX = SUBPAGE_INDEX_CGROUP_RSVD,
-#endif
-#ifdef CONFIG_MEMORY_FAILURE
-	SUBPAGE_INDEX_HWPOISON,
-#endif
-	__NR_USED_SUBPAGE,
-};
+#define __NR_USED_SUBPAGE 3
 
 struct hugepage_subpool {
 	spinlock_t lock;
@@ -722,11 +709,11 @@ extern unsigned int default_hstate_idx;
 
 static inline struct hugepage_subpool *hugetlb_folio_subpool(struct folio *folio)
 {
-	return (void *)folio_get_private_1(folio);
+	return folio->_hugetlb_subpool;
 }
 
 /*
- * hugetlb page subpool pointer located in hpage[1].private
+ * hugetlb page subpool pointer located in hpage[2].hugetlb_subpool
  */
 static inline struct hugepage_subpool *hugetlb_page_subpool(struct page *hpage)
 {
@@ -736,7 +723,7 @@ static inline struct hugepage_subpool *hugetlb_page_subpool(struct page *hpage)
 static inline void hugetlb_set_folio_subpool(struct folio *folio,
 					struct hugepage_subpool *subpool)
 {
-	folio_set_private_1(folio, (unsigned long)subpool);
+	folio->_hugetlb_subpool = subpool;
 }
 
 static inline void hugetlb_set_page_subpool(struct page *hpage,