ring-buffer: Add helper functions for allocations

The allocation of the per CPU buffer descriptor, the buffer page
descriptors and the buffer page data itself can be pretty ugly:

  kzalloc_node(ALIGN(sizeof(struct buffer_page), cache_line_size()),
               GFP_KERNEL, cpu_to_node(cpu));

And the data pages:

  page = alloc_pages_node(cpu_to_node(cpu),
                          GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_COMP | __GFP_ZERO, order);
  if (!page)
	return NULL;
  bpage->page = page_address(page);
  rb_init_page(bpage->page);

Add helper functions to make the code easier to read.

This does make all allocations of the data page (bpage->page) allocated
with the __GFP_RETRY_MAYFAIL flag (and not just the bulk allocator). Which
is actually better, as allocating the data page for the ring buffer tracing
should try hard but not trigger the OOM killer.

Link: https://lore.kernel.org/all/CAHk-=wjMMSAaqTjBSfYenfuzE1bMjLj+2DLtLWJuGt07UGCH_Q@mail.gmail.com/

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20251125121153.35c07461@gandalf.local.home
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: rostedt

kernel/trace/ring_buffer.c

@@ -401,6 +401,41 @@ static void free_buffer_page(struct buffer_page *bpage)
 	kfree(bpage);
 }
 
+/*
+ * For best performance, allocate cpu buffer data cache line sized
+ * and per CPU.
+ */
+#define alloc_cpu_buffer(cpu) (struct ring_buffer_per_cpu *)		\
+	kzalloc_node(ALIGN(sizeof(struct ring_buffer_per_cpu),		\
+			   cache_line_size()), GFP_KERNEL, cpu_to_node(cpu));
+
+#define alloc_cpu_page(cpu) (struct buffer_page *)			\
+	kzalloc_node(ALIGN(sizeof(struct buffer_page),			\
+			   cache_line_size()), GFP_KERNEL, cpu_to_node(cpu));
+
+static struct buffer_data_page *alloc_cpu_data(int cpu, int order)
+{
+	struct buffer_data_page *dpage;
+	struct page *page;
+	gfp_t mflags;
+
+	/*
+	 * __GFP_RETRY_MAYFAIL flag makes sure that the allocation fails
+	 * gracefully without invoking oom-killer and the system is not
+	 * destabilized.
+	 */
+	mflags = GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_COMP | __GFP_ZERO;
+
+	page = alloc_pages_node(cpu_to_node(cpu), mflags, order);
+	if (!page)
+		return NULL;
+
+	dpage = page_address(page);
+	rb_init_page(dpage);
+
+	return dpage;
+}
+
 /*
  * We need to fit the time_stamp delta into 27 bits.
  */
@@ -2204,7 +2239,6 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 	struct ring_buffer_cpu_meta *meta = NULL;
 	struct buffer_page *bpage, *tmp;
 	bool user_thread = current->mm != NULL;
-	gfp_t mflags;
 	long i;
 
 	/*
@@ -2218,13 +2252,6 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 	if (i < nr_pages)
 		return -ENOMEM;
 
-	/*
-	 * __GFP_RETRY_MAYFAIL flag makes sure that the allocation fails
-	 * gracefully without invoking oom-killer and the system is not
-	 * destabilized.
-	 */
-	mflags = GFP_KERNEL | __GFP_RETRY_MAYFAIL;
-
 	/*
 	 * If a user thread allocates too much, and si_mem_available()
 	 * reports there's enough memory, even though there is not.
@@ -2241,10 +2268,8 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 		meta = rb_range_meta(buffer, nr_pages, cpu_buffer->cpu);
 
 	for (i = 0; i < nr_pages; i++) {
-		struct page *page;
 
-		bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
-				    mflags, cpu_to_node(cpu_buffer->cpu));
+		bpage = alloc_cpu_page(cpu_buffer->cpu);
 		if (!bpage)
 			goto free_pages;
 
@@ -2267,13 +2292,10 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 			bpage->range = 1;
 			bpage->id = i + 1;
 		} else {
-			page = alloc_pages_node(cpu_to_node(cpu_buffer->cpu),
-						mflags | __GFP_COMP | __GFP_ZERO,
-						cpu_buffer->buffer->subbuf_order);
-			if (!page)
+			int order = cpu_buffer->buffer->subbuf_order;
+			bpage->page = alloc_cpu_data(cpu_buffer->cpu, order);
+			if (!bpage->page)
 				goto free_pages;
-			bpage->page = page_address(page);
-			rb_init_page(bpage->page);
 		}
 		bpage->order = cpu_buffer->buffer->subbuf_order;
 
@@ -2324,14 +2346,12 @@ static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 static struct ring_buffer_per_cpu *
 rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
 {
-	struct ring_buffer_per_cpu *cpu_buffer __free(kfree) = NULL;
+	struct ring_buffer_per_cpu *cpu_buffer __free(kfree) =
+		alloc_cpu_buffer(cpu);
 	struct ring_buffer_cpu_meta *meta;
 	struct buffer_page *bpage;
-	struct page *page;
 	int ret;
 
-	cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
-				  GFP_KERNEL, cpu_to_node(cpu));
 	if (!cpu_buffer)
 		return NULL;
 
@@ -2347,8 +2367,7 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
 	init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
 	mutex_init(&cpu_buffer->mapping_lock);
 
-	bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
-			    GFP_KERNEL, cpu_to_node(cpu));
+	bpage = alloc_cpu_page(cpu);
 	if (!bpage)
 		return NULL;
 
@@ -2370,13 +2389,10 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
 			rb_meta_buffer_update(cpu_buffer, bpage);
 		bpage->range = 1;
 	} else {
-		page = alloc_pages_node(cpu_to_node(cpu),
-					GFP_KERNEL | __GFP_COMP | __GFP_ZERO,
-					cpu_buffer->buffer->subbuf_order);
-		if (!page)
+		int order = cpu_buffer->buffer->subbuf_order;
+		bpage->page = alloc_cpu_data(cpu, order);
+		if (!bpage->page)
 			goto fail_free_reader;
-		bpage->page = page_address(page);
-		rb_init_page(bpage->page);
 	}
 
 	INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
@@ -6464,7 +6480,6 @@ ring_buffer_alloc_read_page(struct trace_buffer *buffer, int cpu)
 	struct ring_buffer_per_cpu *cpu_buffer;
 	struct buffer_data_read_page *bpage = NULL;
 	unsigned long flags;
-	struct page *page;
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
 		return ERR_PTR(-ENODEV);
@@ -6486,22 +6501,16 @@ ring_buffer_alloc_read_page(struct trace_buffer *buffer, int cpu)
 	arch_spin_unlock(&cpu_buffer->lock);
 	local_irq_restore(flags);
 
-	if (bpage->data)
-		goto out;
-
-	page = alloc_pages_node(cpu_to_node(cpu),
-				GFP_KERNEL | __GFP_NORETRY | __GFP_COMP | __GFP_ZERO,
-				cpu_buffer->buffer->subbuf_order);
-	if (!page) {
-		kfree(bpage);
-		return ERR_PTR(-ENOMEM);
+	if (bpage->data) {
+		rb_init_page(bpage->data);
+	} else {
+		bpage->data = alloc_cpu_data(cpu, cpu_buffer->buffer->subbuf_order);
+		if (!bpage->data) {
+			kfree(bpage);
+			return ERR_PTR(-ENOMEM);
+		}
 	}
 
-	bpage->data = page_address(page);
-
- out:
-	rb_init_page(bpage->data);
-
 	return bpage;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);