Optimize page fault handling by caching last accessed range

kernel-src/include/kernel/mm.h

@@ -46,6 +46,8 @@ typedef struct {
 	rbtree_t *ranges;
 	void *start;
 	void *end;
+
+	mm_range_t *last_pagefault;
 } mm_space_t;
 
 typedef struct {

kernel-src/mm/mm.c

@@ -273,7 +273,13 @@ bool mm_handle_page_fault(void *addr, bool user, int actions) {
 	}
 
 	MUTEX_ACQUIRE(&space->lock);
-	mm_range_t *range = mm_get_range(space, addr);
+
+	// we look at the last page fault range and check if the address is in this range
+	// this might avoid a more expensive tree lookup
+	mm_range_t *range = space->last_pagefault;
+	if (range == NULL || range->start > addr || addr >= range->start + range->size) {
+		range = mm_get_range(space, addr);
+	}
 
 	bool status = false;
 
@@ -282,6 +288,8 @@ bool mm_handle_page_fault(void *addr, bool user, int actions) {
 		goto cleanup;
 	}
 
+	space->last_pagefault = range;
+
 	// check if valid
 
 	int invalid_actions = 0;
@@ -486,8 +494,12 @@ void *mm_map(void *addr, volatile size_t size, int flags, mmuflags_t mmuflags, v
 
 	mm_insert_range(space, range);
 	cleanup:
-	if (ret_addr == NULL && range)
+	if (ret_addr == NULL && range) {
+		if (space->last_pagefault == range)
+			space->last_pagefault = NULL;
+
 		mm_free_range(range);
+	}
 
 	MUTEX_RELEASE(&space->lock);
 	return ret_addr;

kernel-src/mm/range.c

@@ -122,6 +122,9 @@ void mm_insert_range(mm_space_t *space, mm_range_t *new_range) {
 	if (next_range && ranges_compatible(new_range, next_range)) {
 		new_range->size += next_range->size;
 
+		if (space->last_pagefault == next_range)
+			space->last_pagefault = NULL;
+
 		rbtree_remove(&space->ranges, &next_range->rbtree_node);
 		mm_free_range(next_range);
 		if (new_range->flags & MM_RANGE_FLAGS_FILE) {
@@ -133,6 +136,9 @@ void mm_insert_range(mm_space_t *space, mm_range_t *new_range) {
 	if (prev_range && ranges_compatible(prev_range, new_range)) {
 		prev_range->size += new_range->size;
 
+		if (space->last_pagefault == new_range)
+			space->last_pagefault = NULL;
+
 		rbtree_remove(&space->ranges, &new_range->rbtree_node);
 		mm_free_range(new_range);
 		if (prev_range->flags & MM_RANGE_FLAGS_FILE) {
@@ -382,6 +388,9 @@ int mm_change_range(mm_space_t *space, void *address, size_t size, bool free, in
 
 		// remove or change the flags of the range
 		if (free) {
+			if (space->last_pagefault == range)
+				space->last_pagefault = NULL;
+
 			rbtree_remove(&space->ranges, &range->rbtree_node);
 			mm_destroy_range(range, 0, range->size, 0);
 			mm_free_range(range);
@@ -410,8 +419,9 @@ int mm_change_range(mm_space_t *space, void *address, size_t size, bool free, in
 		}
 
 		size_t difference = (uintptr_t)top - (uintptr_t)range->start;
-		if (free)
+		if (free) {
 			mm_destroy_range(range, 0, difference, 0);
+		}
 
 		range->start = (void *)((uintptr_t)range->start + difference);
 		range->size -= difference;