linux-kernel - [PATCH RFC 2/6] mm: PGTABLE_HAS_P[MU]D

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Message-ID: <20240717220219.3743374-3-peterx@redhat.com>
Date: Wed, 17 Jul 2024 18:02:15 -0400
From: Peter Xu <peterx@...hat.com>
To: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Cc: Vlastimil Babka <vbabka@...e.cz>,
	peterx@...hat.com,
	David Hildenbrand <david@...hat.com>,
	Oscar Salvador <osalvador@...e.de>,
	linux-s390@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <willy@...radead.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Michal Hocko <mhocko@...nel.org>,
	linux-riscv@...ts.infradead.org,
	sparclinux@...r.kernel.org,
	Alex Williamson <alex.williamson@...hat.com>,
	Jason Gunthorpe <jgg@...dia.com>,
	x86@...nel.org,
	Alistair Popple <apopple@...dia.com>,
	linuxppc-dev@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org,
	Ryan Roberts <ryan.roberts@....com>,
	Hugh Dickins <hughd@...gle.com>,
	Axel Rasmussen <axelrasmussen@...gle.com>
Subject: [PATCH RFC 2/6] mm: PGTABLE_HAS_P[MU]D_LEAVES config options

Introduce two more sub-options for PGTABLE_HAS_HUGE_LEAVES:

  - PGTABLE_HAS_PMD_LEAVES: set when there can be PMD mappings
  - PGTABLE_HAS_PUD_LEAVES: set when there can be PUD mappings

It will help to identify whether the current build may only want PMD
helpers but not PUD ones, as these sub-options will also check against the
arch support over HAVE_ARCH_TRANSPARENT_HUGEPAGE[_PUD].

Note that having them depend on HAVE_ARCH_TRANSPARENT_HUGEPAGE[_PUD] is
still some intermediate step.  The best way is to have an option say
"whether arch XXX supports PMD/PUD mappings" and so on.  However let's
leave that for later as that's the easy part.  So far, we use these options
to stably detect per-arch huge mapping support.

Signed-off-by: Peter Xu <peterx@...hat.com>
---
 include/linux/huge_mm.h | 10 +++++++---
 mm/Kconfig              |  6 ++++++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 711632df7edf..37482c8445d1 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -96,14 +96,18 @@ extern struct kobj_attribute thpsize_shmem_enabled_attr;
 #define thp_vma_allowable_order(vma, vm_flags, tva_flags, order) \
 	(!!thp_vma_allowable_orders(vma, vm_flags, tva_flags, BIT(order)))
 
-#ifdef CONFIG_PGTABLE_HAS_HUGE_LEAVES
-#define HPAGE_PMD_SHIFT PMD_SHIFT
+#ifdef CONFIG_PGTABLE_HAS_PUD_LEAVES
 #define HPAGE_PUD_SHIFT PUD_SHIFT
 #else
-#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
 #define HPAGE_PUD_SHIFT ({ BUILD_BUG(); 0; })
 #endif
 
+#ifdef CONFIG_PGTABLE_HAS_PMD_LEAVES
+#define HPAGE_PMD_SHIFT PMD_SHIFT
+#else
+#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
+#endif
+
 #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
 #define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
 #define HPAGE_PMD_MASK	(~(HPAGE_PMD_SIZE - 1))
diff --git a/mm/Kconfig b/mm/Kconfig
index 60796402850e..2dbdc088dee8 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -860,6 +860,12 @@ endif # TRANSPARENT_HUGEPAGE
 config PGTABLE_HAS_HUGE_LEAVES
 	def_bool TRANSPARENT_HUGEPAGE || HUGETLB_PAGE
 
+config PGTABLE_HAS_PMD_LEAVES
+	def_bool HAVE_ARCH_TRANSPARENT_HUGEPAGE && PGTABLE_HAS_HUGE_LEAVES
+
+config PGTABLE_HAS_PUD_LEAVES
+	def_bool HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD && PGTABLE_HAS_HUGE_LEAVES
+
 #
 # UP and nommu archs use km based percpu allocator
 #
-- 
2.45.0