Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932746Ab1CRXAU (ORCPT ); Fri, 18 Mar 2011 19:00:20 -0400 Received: from smtp-out.google.com ([74.125.121.67]:59237 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932177Ab1CRXAQ (ORCPT ); Fri, 18 Mar 2011 19:00:16 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type; b=NejJ8tHSlAXKIII6L0glbWa3xcnQXD/TE4M2mYMT1uNim/6eFQESs53RuHNwOih3kk vXc4XX16m2F6unyEq8mg== MIME-Version: 1.0 In-Reply-To: <1300397780.16880.579.camel@gandalf.stny.rr.com> References: <1300397780.16880.579.camel@gandalf.stny.rr.com> From: David Sharp Date: Fri, 18 Mar 2011 15:59:53 -0700 Message-ID: Subject: Re: [RFC] tracing: a proc file to automatically release ring buffer memory To: Steven Rostedt Cc: Vaibhav Nagarnaik , mingo@elte.hu, fweisbec@gmail.com, lizf@cn.fujitsu.com, Michael Rubin , linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2118 Lines: 43 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/