From 64607152ee217c814e601c6a961950e82aa98872 Mon Sep 17 00:00:00 2001
From: Balazs Gerofi <bgerofi@riken.jp>
Date: Wed, 23 Nov 2016 08:48:44 +0900
Subject: [PATCH] VM: introduction of range lookup cache

---
 kernel/include/process.h |  4 ++++
 kernel/process.c         | 33 ++++++++++++++++++++++++++++++++-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/kernel/include/process.h b/kernel/include/process.h
index 7e96f978..503e27ba 100644
--- a/kernel/include/process.h
+++ b/kernel/include/process.h
@@ -643,6 +643,8 @@ struct thread {
 	struct waitq scd_wq;
 };
 
+#define VM_RANGE_CACHE_SIZE	4
+
 struct process_vm {
 	struct address_space *address_space;
 	struct list_head vm_range_list;
@@ -669,6 +671,8 @@ struct process_vm {
 	int numa_mem_policy;
 	/* Protected by memory_range_lock */
 	struct list_head vm_range_numa_policy_list;
+	struct vm_range *range_cache[VM_RANGE_CACHE_SIZE];
+	int range_cache_ind;
 };
 
 static inline int has_cap_ipc_lock(struct thread *th)
diff --git a/kernel/process.c b/kernel/process.c
index 90821717..e7f4f751 100644
--- a/kernel/process.c
+++ b/kernel/process.c
@@ -226,6 +226,11 @@ init_process_vm(struct process *owner, struct address_space *asp, struct process
 	}
 	vm->numa_mem_policy = MPOL_DEFAULT;
 
+	for (i = 0; i < VM_RANGE_CACHE_SIZE; ++i) {
+		vm->range_cache[i] = NULL;
+	}
+	vm->range_cache_ind = 0;
+
 	return 0;
 }
 
@@ -734,6 +739,7 @@ int join_process_memory_range(struct process_vm *vm,
 		struct vm_range *surviving, struct vm_range *merging)
 {
 	int error;
+	int i;
 
 	dkprintf("join_process_memory_range(%p,%lx-%lx,%lx-%lx)\n",
 			vm, surviving->start, surviving->end,
@@ -762,6 +768,10 @@ int join_process_memory_range(struct process_vm *vm,
 		memobj_release(merging->memobj);
 	}
 	list_del(&merging->list);
+	for (i = 0; i < VM_RANGE_CACHE_SIZE; ++i) {
+		if (vm->range_cache[i] == merging)
+			vm->range_cache[i] = surviving;
+	}
 	kfree(merging);
 
 	error = 0;
@@ -775,7 +785,7 @@ int free_process_memory_range(struct process_vm *vm, struct vm_range *range)
 {
 	const intptr_t start0 = range->start;
 	const intptr_t end0 = range->end;
-	int error;
+	int error, i;
 	intptr_t start;
 	intptr_t end;
 	struct vm_range *neighbor;
@@ -860,6 +870,10 @@ int free_process_memory_range(struct process_vm *vm, struct vm_range *range)
 	}
 
 	list_del(&range->list);
+	for (i = 0; i < VM_RANGE_CACHE_SIZE; ++i) {
+		if (vm->range_cache[i] == range)
+			vm->range_cache[i] = NULL;
+	}
 	kfree(range);
 
 	dkprintf("free_process_memory_range(%p,%lx-%lx): 0\n",
@@ -1076,6 +1090,7 @@ int add_process_memory_range(struct process_vm *vm,
 struct vm_range *lookup_process_memory_range(
 		struct process_vm *vm, uintptr_t start, uintptr_t end)
 {
+	int i;
 	struct vm_range *range = NULL;
 
 	dkprintf("lookup_process_memory_range(%p,%lx,%lx)\n", vm, start, end);
@@ -1084,6 +1099,16 @@ struct vm_range *lookup_process_memory_range(
 		goto out;
 	}
 
+	for (i = 0; i < VM_RANGE_CACHE_SIZE; ++i) {
+		int c_i = (i + vm->range_cache_ind) % VM_RANGE_CACHE_SIZE;
+		if (!vm->range_cache[c_i])
+			continue;
+
+		if (vm->range_cache[c_i]->start <= start &&
+			vm->range_cache[c_i]->end >= end)
+			return vm->range_cache[c_i];
+	}
+
 	list_for_each_entry(range, &vm->vm_range_list, list) {
 		if (end <= range->start) {
 			break;
@@ -1095,6 +1120,12 @@ struct vm_range *lookup_process_memory_range(
 
 	range = NULL;
 out:
+	if (range) {
+		vm->range_cache_ind = (vm->range_cache_ind - 1 + VM_RANGE_CACHE_SIZE)
+			% VM_RANGE_CACHE_SIZE;
+		vm->range_cache[vm->range_cache_ind] = range;
+	}
+
 	dkprintf("lookup_process_memory_range(%p,%lx,%lx): %p %lx-%lx\n",
 			vm, start, end, range,
 			range? range->start: 0, range? range->end: 0);