ftrace: Allocate the mcount record pages as groups

Allocate the mcount record pages as a group of pages as big
as can be allocated and waste no more than a single page.

Grouping the mcount pages as much as possible helps with cache
locality, as we do not need to redirect with descriptors as we
cross from page to page. It also allows us to do more with the
records later on (sort them with bigger benefits).
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ftrace.c

@@ -983,12 +983,13 @@ static DEFINE_MUTEX(ftrace_regex_lock);
 
 struct ftrace_page {
 	struct ftrace_page	*next;
+	struct dyn_ftrace	*records;
 	int			index;
-	struct dyn_ftrace	records[];
+	int			size;
 };
 
-#define ENTRIES_PER_PAGE \
-  ((PAGE_SIZE - sizeof(struct ftrace_page)) / sizeof(struct dyn_ftrace))
+#define ENTRY_SIZE sizeof(struct dyn_ftrace)
+#define ENTRIES_PER_PAGE (PAGE_SIZE / ENTRY_SIZE)
 
 /* estimate from running different kernels */
 #define NR_TO_INIT		10000
@@ -1421,14 +1422,10 @@ static void ftrace_hash_rec_enable(struct ftrace_ops *ops,
 
 static struct dyn_ftrace *ftrace_alloc_dyn_node(unsigned long ip)
 {
-	if (ftrace_pages->index == ENTRIES_PER_PAGE) {
-		if (!ftrace_pages->next) {
-			/* allocate another page */
-			ftrace_pages->next =
-				(void *)get_zeroed_page(GFP_KERNEL);
-			if (!ftrace_pages->next)
-				return NULL;
-		}
+	if (ftrace_pages->index == ftrace_pages->size) {
+		/* We should have allocated enough */
+		if (WARN_ON(!ftrace_pages->next))
+			return NULL;
 		ftrace_pages = ftrace_pages->next;
 	}
 
@@ -2005,47 +2002,106 @@ static int ftrace_update_code(struct module *mod)
 	return 0;
 }
 
-static int __init ftrace_dyn_table_alloc(unsigned long num_to_init)
+static int ftrace_allocate_records(struct ftrace_page *pg, int count)
 {
-	struct ftrace_page *pg;
+	int order;
 	int cnt;
-	int i;
 
-	/* allocate a few pages */
-	ftrace_pages_start = (void *)get_zeroed_page(GFP_KERNEL);
-	if (!ftrace_pages_start)
-		return -1;
+	if (WARN_ON(!count))
+		return -EINVAL;
+
+	order = get_count_order(DIV_ROUND_UP(count, ENTRIES_PER_PAGE));
 
 	/*
-	 * Allocate a few more pages.
-	 *
-	 * TODO: have some parser search vmlinux before
-	 *   final linking to find all calls to ftrace.
-	 *   Then we can:
-	 *    a) know how many pages to allocate.
-	 *     and/or
-	 *    b) set up the table then.
-	 *
-	 *  The dynamic code is still necessary for
-	 *  modules.
+	 * We want to fill as much as possible. No more than a page
+	 * may be empty.
 	 */
+	while ((PAGE_SIZE << order) / ENTRY_SIZE >= count + ENTRIES_PER_PAGE)
+		order--;
 
-	pg = ftrace_pages = ftrace_pages_start;
+ again:
+	pg->records = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
 
-	cnt = num_to_init / ENTRIES_PER_PAGE;
-	pr_info("ftrace: allocating %ld entries in %d pages\n",
-		num_to_init, cnt + 1);
+	if (!pg->records) {
+		/* if we can't allocate this size, try something smaller */
+		if (!order)
+			return -ENOMEM;
+		order >>= 1;
+		goto again;
+	}
 
-	for (i = 0; i < cnt; i++) {
-		pg->next = (void *)get_zeroed_page(GFP_KERNEL);
+	cnt = (PAGE_SIZE << order) / ENTRY_SIZE;
+	pg->size = cnt;
 
-		/* If we fail, we'll try later anyway */
-		if (!pg->next)
+	if (cnt > count)
+		cnt = count;
+
+	return cnt;
+}
+
+static struct ftrace_page *
+ftrace_allocate_pages(unsigned long num_to_init)
+{
+	struct ftrace_page *start_pg;
+	struct ftrace_page *pg;
+	int order;
+	int cnt;
+
+	if (!num_to_init)
+		return 0;
+
+	start_pg = pg = kzalloc(sizeof(*pg), GFP_KERNEL);
+	if (!pg)
+		return NULL;
+
+	/*
+	 * Try to allocate as much as possible in one continues
+	 * location that fills in all of the space. We want to
+	 * waste as little space as possible.
+	 */
+	for (;;) {
+		cnt = ftrace_allocate_records(pg, num_to_init);
+		if (cnt < 0)
+			goto free_pages;
+
+		num_to_init -= cnt;
+		if (!num_to_init)
 			break;
 
+		pg->next = kzalloc(sizeof(*pg), GFP_KERNEL);
+		if (!pg->next)
+			goto free_pages;
+
 		pg = pg->next;
 	}
 
+	return start_pg;
+
+ free_pages:
+	while (start_pg) {
+		order = get_count_order(pg->size / ENTRIES_PER_PAGE);
+		free_pages((unsigned long)pg->records, order);
+		start_pg = pg->next;
+		kfree(pg);
+		pg = start_pg;
+	}
+	pr_info("ftrace: FAILED to allocate memory for functions\n");
+	return NULL;
+}
+
+static int __init ftrace_dyn_table_alloc(unsigned long num_to_init)
+{
+	int cnt;
+
+	if (!num_to_init) {
+		pr_info("ftrace: No functions to be traced?\n");
+		return -1;
+	}
+
+	cnt = num_to_init / ENTRIES_PER_PAGE;
+	pr_info("ftrace: allocating %ld entries in %d pages\n",
+		num_to_init, cnt + 1);
+
 	return 0;
 }
 
@@ -3520,30 +3576,45 @@ static int ftrace_process_locs(struct module *mod,
 			       unsigned long *start,
 			       unsigned long *end)
 {
+	struct ftrace_page *pg;
+	unsigned long count;
 	unsigned long *p;
 	unsigned long addr;
 	unsigned long flags = 0; /* Shut up gcc */
+	int ret = -ENOMEM;
+
+	count = end - start;
+
+	if (!count)
+		return 0;
+
+	pg = ftrace_allocate_pages(count);
+	if (!pg)
+		return -ENOMEM;
 
 	mutex_lock(&ftrace_lock);
+
 	/*
 	 * Core and each module needs their own pages, as
 	 * modules will free them when they are removed.
 	 * Force a new page to be allocated for modules.
 	 */
-	if (mod) {
+	if (!mod) {
+		WARN_ON(ftrace_pages || ftrace_pages_start);
+		/* First initialization */
+		ftrace_pages = ftrace_pages_start = pg;
+	} else {
 		if (!ftrace_pages)
-			return -ENOMEM;
+			goto out;
 
-		/*
-		 * If the last page was full, it will be
-		 * allocated anyway.
-		 */
-		if (ftrace_pages->index != ENTRIES_PER_PAGE) {
-			ftrace_pages->next = (void *)get_zeroed_page(GFP_KERNEL);
-			if (!ftrace_pages->next)
-				return -ENOMEM;
-			ftrace_pages = ftrace_pages->next;
+		if (WARN_ON(ftrace_pages->next)) {
+			/* Hmm, we have free pages? */
+			while (ftrace_pages->next)
+				ftrace_pages = ftrace_pages->next;
 		}
+
+		ftrace_pages->next = pg;
+		ftrace_pages = pg;
 	}
 
 	p = start;
@@ -3557,7 +3628,8 @@ static int ftrace_process_locs(struct module *mod,
 		 */
 		if (!addr)
 			continue;
-		ftrace_record_ip(addr);
+		if (!ftrace_record_ip(addr))
+			break;
 	}
 
 	/*
@@ -3573,9 +3645,11 @@ static int ftrace_process_locs(struct module *mod,
 	ftrace_update_code(mod);
 	if (!mod)
 		local_irq_restore(flags);
+	ret = 0;
+ out:
 	mutex_unlock(&ftrace_lock);
 
-	return 0;
+	return ret;
 }
 
 #ifdef CONFIG_MODULES
@@ -3587,6 +3661,7 @@ void ftrace_release_mod(struct module *mod)
 	struct dyn_ftrace *rec;
 	struct ftrace_page **last_pg;
 	struct ftrace_page *pg;
+	int order;
 
 	mutex_lock(&ftrace_lock);
 
@@ -3613,7 +3688,9 @@ void ftrace_release_mod(struct module *mod)
 				ftrace_pages = next_to_ftrace_page(last_pg);
 
 			*last_pg = pg->next;
-			free_page((unsigned long)pg);
+			order = get_count_order(pg->size / ENTRIES_PER_PAGE);
+			free_pages((unsigned long)pg->records, order);
+			kfree(pg);
 		} else
 			last_pg = &pg->next;
 	}