This patch introduces a new swap entry type called PTE_MARKER. It can be
installed for any pte that maps a file-backed memory when the pte is
temporarily zapped, so as to maintain per-pte information.
The information that kept in the pte is called a "marker". Here we define the
marker as "unsigned long" just to match pgoff_t, however it will only work if
it still fits in swp_offset(), which is e.g. currently 58 bits on x86_64.
The first marker bit that is introduced together with the new swap pte is the
PAGEOUT marker. When that bit is set, it means this pte used to point to a
page which got swapped out. It's mostly a definition so the swap type is not
totally nothing, however the functions are not implemented yet to handle the
new swap type.
A new config CONFIG_PTE_MARKER is introduced too; it's by default off.
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
include/linux/swap.h | 14 ++++++++++++-
include/linux/swapops.h | 45 +++++++++++++++++++++++++++++++++++++++++
mm/Kconfig | 17 ++++++++++++++++
3 files changed, 75 insertions(+), 1 deletion(-)
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 6f5a43251593..545dc8e0b0fb 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -55,6 +55,18 @@ static inline int current_is_kswapd(void)
* actions on faults.
*/
+/*
+ * PTE markers are used to persist information onto PTEs that are mapped with
+ * file-backed memories.
+ */
+#ifdef CONFIG_PTE_MARKER
+#define SWP_PTE_MARKER_NUM 1
+#define SWP_PTE_MARKER (MAX_SWAPFILES + SWP_HWPOISON_NUM + \
+ SWP_MIGRATION_NUM + SWP_DEVICE_NUM)
+#else
+#define SWP_PTE_MARKER_NUM 0
+#endif
+
/*
* Unaddressable device memory support. See include/linux/hmm.h and
* Documentation/vm/hmm.rst. Short description is we need struct pages for
@@ -100,7 +112,7 @@ static inline int current_is_kswapd(void)
#define MAX_SWAPFILES \
((1 << MAX_SWAPFILES_SHIFT) - SWP_DEVICE_NUM - \
- SWP_MIGRATION_NUM - SWP_HWPOISON_NUM)
+ SWP_MIGRATION_NUM - SWP_HWPOISON_NUM - SWP_PTE_MARKER_NUM)
/*
* Magic header for a swap area. The first part of the union is
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index d356ab4047f7..3fec83449e1e 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -247,6 +247,51 @@ static inline int is_writable_migration_entry(swp_entry_t entry)
#endif
+#ifdef CONFIG_PTE_MARKER
+
+#ifdef CONFIG_PTE_MARKER_PAGEOUT
+/* When this bit is set, it means this page is swapped out previously */
+#define PTE_MARKER_PAGEOUT (1UL << 0)
+#else
+#define PTE_MARKER_PAGEOUT 0
+#endif
+
+#define PTE_MARKER_MASK (PTE_MARKER_PAGEOUT)
+
+static inline swp_entry_t make_pte_marker_entry(unsigned long marker)
+{
+ return swp_entry(SWP_PTE_MARKER, marker);
+}
+
+static inline bool is_pte_marker_entry(swp_entry_t entry)
+{
+ return swp_type(entry) == SWP_PTE_MARKER;
+}
+
+static inline unsigned long pte_marker_get(swp_entry_t entry)
+{
+ return swp_offset(entry) & PTE_MARKER_MASK;
+}
+
+#else /* CONFIG_PTE_MARKER */
+
+static inline swp_entry_t make_pte_marker_entry(unsigned long marker)
+{
+ return swp_entry(0, 0);
+}
+
+static inline bool is_pte_marker_entry(swp_entry_t entry)
+{
+ return false;
+}
+
+static inline unsigned long pte_marker_get(swp_entry_t entry)
+{
+ return 0;
+}
+
+#endif /* CONFIG_PTE_MARKER */
+
static inline struct page *pfn_swap_entry_to_page(swp_entry_t entry)
{
struct page *p = pfn_to_page(swp_offset(entry));
diff --git a/mm/Kconfig b/mm/Kconfig
index 40a9bfcd5062..6043d8f1c066 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -889,4 +889,21 @@ config IO_MAPPING
config SECRETMEM
def_bool ARCH_HAS_SET_DIRECT_MAP && !EMBEDDED
+config PTE_MARKER
+ def_bool n
+ bool "Marker PTEs support"
+
+ help
+ Allows to create marker PTEs for file-backed memory.
+
+config PTE_MARKER_PAGEOUT
+ def_bool n
+ depends on PTE_MARKER
+ bool "Shmem pagemap PM_SWAP support"
+
+ help
+ Allows to create marker PTEs for file-backed memory when the page is
+ swapped out. It's required for pagemap to work correctly with shmem
+ on page swapping.
+
endmenu
--
2.32.0
