From dad6a5eb55564845aa17b8b20fa834af21e46c48 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Wed, 2 Nov 2022 18:48:45 -0700 Subject: 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 Acked-by: Kirill A. Shutemov Cc: David Hildenbrand Cc: James Houghton Cc: John Hubbard Cc: Matthew Wilcox (Oracle) Cc: Miaohe Lin Cc: Mike Kravetz Cc: Mina Almasry Cc: Muchun Song Cc: Naoya Horiguchi Cc: Peter Xu Cc: Sidhartha Kumar Cc: Vlastimil Babka Cc: Yang Shi Cc: Zach O'Keefe Signed-off-by: Andrew Morton --- mm/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'mm/Kconfig') 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 -- cgit