[RFC PATCH V3 15/17] prctl: Introduce new prctl to control scanning

[Raghavendra K T <raghavendra.kt@amd.com>]

 A new scalar value (PTEAScanScale) to control per task PTE A bit scanning
is introduced.

0    : scanning disabled
1-10 : scanning enabled.

In future PTEAScanScale could be used to control aggressiveness of
scanning.

CC: linux-doc@vger.kernel.org
CC: Jonathan Corbet <corbet@lwn.net>
CC: linux-fsdevel@vger.kernel.org

Suggested-by: David Rientjes <rientjes@google.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@amd.com>
---
 Documentation/filesystems/proc.rst |  2 ++
 fs/proc/task_mmu.c                 |  4 ++++
 include/linux/mm_types.h           |  3 +++
 include/uapi/linux/prctl.h         |  7 +++++++
 kernel/fork.c                      |  4 ++++
 kernel/sys.c                       | 25 +++++++++++++++++++++++++
 mm/kscand.c                        |  5 +++++
 7 files changed, 50 insertions(+)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 5236cb52e357..0e99d1ca229a 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -205,6 +205,7 @@ read the file /proc/PID/status::
   VmLib:      1412 kB
   VmPTE:        20 kb
   VmSwap:        0 kB
+  PTEAScanScale: 0
   HugetlbPages:          0 kB
   CoreDumping:    0
   THP_enabled:	  1
@@ -288,6 +289,7 @@ It's slow but very precise.
  VmPTE                       size of page table entries
  VmSwap                      amount of swap used by anonymous private data
                              (shmem swap usage is not included)
+ PTEAScanScale               Integer representing async PTE A bit scan agrression
  HugetlbPages                size of hugetlb memory portions
  CoreDumping                 process's memory is currently being dumped
                              (killing the process may lead to a corrupted core)
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 751479eb128f..05be24e4bc4f 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -79,6 +79,10 @@ void task_mem(struct seq_file *m, struct mm_struct *mm)
 		    " kB\nVmPTE:\t", mm_pgtables_bytes(mm) >> 10, 8);
 	SEQ_PUT_DEC(" kB\nVmSwap:\t", swap);
 	seq_puts(m, " kB\n");
+#ifdef CONFIG_KSCAND
+	seq_put_decimal_ull_width(m, "PTEAScanScale:\t", mm->pte_scan_scale, 8);
+	seq_puts(m, "\n");
+#endif
 	hugetlb_report_usage(m, mm);
 }
 #undef SEQ_PUT_DEC
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index e3d8f11a5a04..798e6053eebe 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1151,6 +1151,9 @@ struct mm_struct {
 #ifdef CONFIG_KSCAND
 		/* Tracks promotion node. XXX: use nodemask */
 		int target_node;
+
+		/* Integer representing PTE A bit scan aggression (0-10) */
+		unsigned int pte_scan_scale;
  #endif
 		/*
 		 * An operation with batched TLB flushing is going on. Anything
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 43dec6eed559..6b5877865e08 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -371,4 +371,11 @@ struct prctl_mm_map {
 # define PR_FUTEX_HASH_GET_SLOTS	2
 # define PR_FUTEX_HASH_GET_IMMUTABLE	3
 
+/* Set/get PTE A bit scan scale */
+#define PR_SET_PTE_A_SCAN_SCALE		79
+#define PR_GET_PTE_A_SCAN_SCALE		80
+# define PR_PTE_A_SCAN_SCALE_MIN	0
+# define PR_PTE_A_SCAN_SCALE_MAX	10
+# define PR_PTE_A_SCAN_SCALE_DEFAULT	8
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index a13043de91b0..bb780215024c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -106,6 +106,7 @@
 #include <uapi/linux/pidfd.h>
 #include <linux/pidfs.h>
 #include <linux/tick.h>
+#include <linux/prctl.h>
 
 #include <asm/pgalloc.h>
 #include <linux/uaccess.h>
@@ -1050,6 +1051,9 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
 	futex_mm_init(mm);
 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !defined(CONFIG_SPLIT_PMD_PTLOCKS)
 	mm->pmd_huge_pte = NULL;
+#endif
+#ifdef CONFIG_KSCAND
+	mm->pte_scan_scale = PR_PTE_A_SCAN_SCALE_DEFAULT;
 #endif
 	mm_init_uprobes_state(mm);
 	hugetlb_count_init(mm);
diff --git a/kernel/sys.c b/kernel/sys.c
index adc0de0aa364..f6c893b22bc6 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2147,6 +2147,19 @@ static int prctl_set_auxv(struct mm_struct *mm, unsigned long addr,
 
 	return 0;
 }
+#ifdef CONFIG_KSCAND
+static int prctl_pte_scan_scale_write(unsigned int scale)
+{
+	scale = clamp(scale, PR_PTE_A_SCAN_SCALE_MIN, PR_PTE_A_SCAN_SCALE_MAX);
+	current->mm->pte_scan_scale = scale;
+	return 0;
+}
+
+static unsigned int prctl_pte_scan_scale_read(void)
+{
+	return current->mm->pte_scan_scale;
+}
+#endif
 
 static int prctl_set_mm(int opt, unsigned long addr,
 			unsigned long arg4, unsigned long arg5)
@@ -2824,6 +2837,18 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 	case PR_FUTEX_HASH:
 		error = futex_hash_prctl(arg2, arg3, arg4);
 		break;
+#ifdef CONFIG_KSCAND
+	case PR_SET_PTE_A_SCAN_SCALE:
+		if (arg3 || arg4 || arg5)
+			return -EINVAL;
+		error = prctl_pte_scan_scale_write((unsigned int) arg2);
+		break;
+	case PR_GET_PTE_A_SCAN_SCALE:
+		if (arg2 || arg3 || arg4 || arg5)
+			return -EINVAL;
+		error = prctl_pte_scan_scale_read();
+		break;
+#endif
 	default:
 		trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5);
 		error = -EINVAL;
diff --git a/mm/kscand.c b/mm/kscand.c
index 273306f47553..8aef6021c6ba 100644
--- a/mm/kscand.c
+++ b/mm/kscand.c
@@ -1306,6 +1306,11 @@ static unsigned long kscand_scan_mm_slot(void)
 		goto outerloop;
 	}
 
+	if (!mm->pte_scan_scale) {
+		next_mm = true;
+		goto outerloop;
+	}
+
 	mm_target_node = READ_ONCE(mm->target_node);
 	if (mm_target_node != mm_slot_target_node)
 		WRITE_ONCE(mm->target_node, mm_slot_target_node);
-- 
2.34.1