Messages in this thread | | | Subject | Re: [RFC] tracing: a proc file to automatically release ring buffer memory | From | Steven Rostedt <> | Date | Thu, 17 Mar 2011 17:36:20 -0400 |
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On Thu, 2011-03-17 at 14:29 -0700, Vaibhav Nagarnaik wrote: > All > > The current way to release memory from ftrace ring buffer is to: > echo 0 > /sys/kernel/debug/tracing/buffer_size_kb > > Consider a scenario where ftrace is handled by a user space > process. Normally, this tracing is done as a low priority task on the > system. Under memory pressure for high priority tasks, tracing should > be turned off and the trace ring buffer memory released. The buffer > allocated is kernel memory and under OOM condition if the user space > process is oom-killed, there is no way to release the ring buffer > memory. > > The proposal is to add a proc entry > /sys/kernel/debug/tracing/buffer_free. Its .release() fileops function > executes tracing_stop() and then resizes the global trace buffer to > minimum size (2*BUF_PAGE_SIZE). The user space process opens this file > and keeps it open. When the process gets killed, the fd gets closed > and .release() is called. This automatically stops the tracing and > frees up the ring buffer memory. > > It is optional to use this functionality, since it won't affect > tracing for current programs. But it provides a way to automatically > free up memory, if needed. It can also be used on the command line to > stop tracing and free up memory as a single operation as: > echo > /sys/kernel/debug/tracing/buffer_free
I don't like adding new files to debug/tracing. If we do add this feature, I rather have it done with the buffer_size_kb directly. Perhaps add an ioctl() to the file that will do this.
You can open it and then ioctl(RINGBUF_FREE_ON_CLOSE);
If the process dies, it closes the buffer_size_kb and frees the memory.
-- Steve
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