ftrace: limit trace entries
Currently there is no protection from the root user to use up all of
memory for trace buffers. If the root user allocates too many entries,
the OOM killer might start kill off all tasks.
This patch adds an algorith to check the following condition:
pages_requested > (freeable_memory + current_trace_buffer_pages) / 4
If the above is met then the allocation fails. The above prevents more
than 1/4th of freeable memory from being used by trace buffers.
To determine the freeable_memory, I made determine_dirtyable_memory in
mm/page-writeback.c global.
Special thanks goes to Peter Zijlstra for suggesting the above calculation.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index f462439..bd91987 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -105,6 +105,8 @@
extern int block_dump;
extern int laptop_mode;
+extern unsigned long determine_dirtyable_memory(void);
+
extern int dirty_ratio_handler(struct ctl_table *table, int write,
struct file *filp, void __user *buffer, size_t *lenp,
loff_t *ppos);