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    SubjectRe: [RFC] tracing: a proc file to automatically release ring buffer memory
    On Thu, Mar 17, 2011 at 2:36 PM, Steven Rostedt <> wrote:
    > 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.

    Thanks for the feedback Steve. An ioctl on buffer_size_kb sounds fine to me.

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