Add the generic 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 version
suits all those architectures which use an unfragmented page for one page
table (none of whose pte_free()s use the mm arg which was passed to it).
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---
include/linux/mm_types.h | 4 ++++
include/linux/pgtable.h | 2 ++
mm/pgtable-generic.c | 20 ++++++++++++++++++++
3 files changed, 26 insertions(+)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 1667a1bdb8a8..09335fa28c41 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -144,6 +144,10 @@ struct page {
struct { /* Page table pages */
unsigned long _pt_pad_1; /* compound_head */
pgtable_t pmd_huge_pte; /* protected by page->ptl */
+ /*
+ * A PTE page table page might be freed by use of
+ * rcu_head: which overlays those two fields above.
+ */
unsigned long _pt_pad_2; /* mapping */
union {
struct mm_struct *pt_mm; /* x86 pgd, s390 */
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 525f1782b466..d18d3e963967 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -112,6 +112,8 @@ static inline void pte_unmap(pte_t *pte)
}
#endif
+void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable);
+
/* Find an entry in the second-level page table.. */
#ifndef pmd_offset
static inline pmd_t *pmd_offset(pud_t *pud, unsigned long address)
diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
index 5e85a625ab30..ab3741064bb8 100644
--- a/mm/pgtable-generic.c
+++ b/mm/pgtable-generic.c
@@ -13,6 +13,7 @@
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/mm_inline.h>
+#include <asm/pgalloc.h>
#include <asm/tlb.h>
/*
@@ -230,6 +231,25 @@ pmd_t pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long address,
return pmd;
}
#endif
+
+/* arch define pte_free_defer in asm/pgalloc.h for its own implementation */
+#ifndef pte_free_defer
+static void pte_free_now(struct rcu_head *head)
+{
+ struct page *page;
+
+ page = container_of(head, struct page, rcu_head);
+ pte_free(NULL /* mm not passed and not used */, (pgtable_t)page);
+}
+
+void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable)
+{
+ struct page *page;
+
+ page = pgtable;
+ call_rcu(&page->rcu_head, pte_free_now);
+}
+#endif /* pte_free_defer */
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
#if defined(CONFIG_GUP_GET_PXX_LOW_HIGH) && \
--
2.35.3
