linux-kernel - [PATCH v2 06/12] sparc: add pte_free_defer() for pte_t *pgtable

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Message-ID: <cb3feef8-f49e-7a54-a6d6-2e9b188f7564@google.com>
Date:   Tue, 20 Jun 2023 00:49:34 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
cc:     Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
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        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH v2 06/12] sparc: add pte_free_defer() for pte_t *pgtable_t

Add sparc-specific pte_free_defer(), to call pte_free() via call_rcu().
pte_free_defer() will be called inside khugepaged's retract_page_tables()
loop, where allocating extra memory cannot be relied upon.  This precedes
the generic version to avoid build breakage from incompatible pgtable_t.

sparc32 supports pagetables sharing a page, but does not support THP;
sparc64 supports THP, but does not support pagetables sharing a page.
So the sparc-specific pte_free_defer() is as simple as the generic one,
except for converting between pte_t *pgtable_t and struct page *.

Signed-off-by: Hugh Dickins <hughd@...gle.com>
---
 arch/sparc/include/asm/pgalloc_64.h |  4 ++++
 arch/sparc/mm/init_64.c             | 16 ++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/arch/sparc/include/asm/pgalloc_64.h b/arch/sparc/include/asm/pgalloc_64.h
index 7b5561d17ab1..caa7632be4c2 100644
--- a/arch/sparc/include/asm/pgalloc_64.h
+++ b/arch/sparc/include/asm/pgalloc_64.h
@@ -65,6 +65,10 @@ pgtable_t pte_alloc_one(struct mm_struct *mm);
 void pte_free_kernel(struct mm_struct *mm, pte_t *pte);
 void pte_free(struct mm_struct *mm, pgtable_t ptepage);
 
+/* arch use pte_free_defer() implementation in arch/sparc/mm/init_64.c */
+#define pte_free_defer pte_free_defer
+void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable);
+
 #define pmd_populate_kernel(MM, PMD, PTE)	pmd_set(MM, PMD, PTE)
 #define pmd_populate(MM, PMD, PTE)		pmd_set(MM, PMD, PTE)
 
diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
index 04f9db0c3111..0d7fd793924c 100644
--- a/arch/sparc/mm/init_64.c
+++ b/arch/sparc/mm/init_64.c
@@ -2930,6 +2930,22 @@ void pgtable_free(void *table, bool is_page)
 }
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static void pte_free_now(struct rcu_head *head)
+{
+	struct page *page;
+
+	page = container_of(head, struct page, rcu_head);
+	__pte_free((pgtable_t)page_address(page));
+}
+
+void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable)
+{
+	struct page *page;
+
+	page = virt_to_page(pgtable);
+	call_rcu(&page->rcu_head, pte_free_now);
+}
+
 void update_mmu_cache_pmd(struct vm_area_struct *vma, unsigned long addr,
 			  pmd_t *pmd)
 {
-- 
2.35.3