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Subject[PATCH 12/12 v2] ring-buffer: Add cached pages when freeing reader page
From: Steven Rostedt <srostedt@redhat.com>

When the pages are removed from the ring buffer for things like
splice they are freed with ring_buffer_free_read_page().
They are also allocated with ring_buffer_alloc_read_page().

Currently the ring buffer does not take advantage of this situation.
Every time the page is freed, the ring buffer simply frees it.
When a new page is needed, it allocates it. This means that reading
several pages with splice will cause a page to be freed and allocated
several times. This is simply a waste.

This patch adds a cache of the pages freed (16 max). This allows
the pages to be reused quickly without need to go back to the memory
pool.

Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/trace/ring_buffer.c | 41 +++++++++++++++++++++++++++++++++++------
1 files changed, 35 insertions(+), 6 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 7f6059c..40667b2 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -157,6 +157,8 @@ static unsigned long ring_buffer_flags __read_mostly = RB_BUFFERS_ON;

#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)

+#define RB_MAX_FREE_PAGES 16
+
/**
* tracing_on - enable all tracing buffers
*
@@ -325,7 +327,10 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data);
#define RB_MISSED_STORED (1 << 30)

struct buffer_data_page {
- u64 time_stamp; /* page time stamp */
+ union {
+ struct buffer_data_page *next; /* for free pages */
+ u64 time_stamp; /* page time stamp */
+ };
local_t commit; /* write committed index */
unsigned char data[]; /* data of buffer page */
};
@@ -472,6 +477,9 @@ struct ring_buffer {
atomic_t record_disabled;
cpumask_var_t cpumask;

+ struct buffer_data_page *free_pages;
+ int nr_free_pages;
+
struct lock_class_key *reader_lock_key;

struct mutex mutex;
@@ -1184,6 +1192,7 @@ EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
void
ring_buffer_free(struct ring_buffer *buffer)
{
+ struct buffer_data_page *bpage;
int cpu;

get_online_cpus();
@@ -1200,6 +1209,11 @@ ring_buffer_free(struct ring_buffer *buffer)
kfree(buffer->buffers);
free_cpumask_var(buffer->cpumask);

+ while (buffer->free_pages) {
+ bpage = buffer->free_pages;
+ buffer->free_pages = bpage->next;
+ free_page((unsigned long)bpage);
+ };
kfree(buffer);
}
EXPORT_SYMBOL_GPL(ring_buffer_free);
@@ -3717,11 +3731,17 @@ void *ring_buffer_alloc_read_page(struct ring_buffer *buffer)
struct buffer_data_page *bpage;
unsigned long addr;

- addr = __get_free_page(GFP_KERNEL);
- if (!addr)
- return NULL;
+ if (!buffer->free_pages) {
+ addr = __get_free_page(GFP_KERNEL);
+ if (!addr)
+ return NULL;

- bpage = (void *)addr;
+ bpage = (void *)addr;
+ } else {
+ bpage = buffer->free_pages;
+ buffer->free_pages = bpage->next;
+ buffer->nr_free_pages--;
+ }

rb_init_page(bpage);

@@ -3738,7 +3758,16 @@ EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
*/
void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
{
- free_page((unsigned long)data);
+ struct buffer_data_page *bpage = data;
+
+ if (buffer->nr_free_pages >= RB_MAX_FREE_PAGES) {
+ free_page((unsigned long)data);
+ return;
+ }
+
+ bpage->next = buffer->free_pages;
+ buffer->free_pages = bpage;
+ buffer->nr_free_pages++;
}
EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);

--
1.7.0



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