From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with SMTP id CEBDF6B0217 for ; Tue, 18 May 2010 11:16:29 -0400 (EDT) Date: Tue, 18 May 2010 11:16:26 -0400 From: Mathieu Desnoyers Subject: Re: [RFC] Tracer Ring Buffer splice() vs page cache [was: Re: Perf and ftrace [was Re: PyTimechart]] Message-ID: <20100518151626.GA7748@Krystal> References: <20100514183242.GA11795@Krystal> <1273862945.1674.14.camel@laptop> <20100517224243.GA10603@Krystal> <1274185160.5605.7787.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1274185160.5605.7787.camel@twins> Sender: owner-linux-mm@kvack.org To: Peter Zijlstra Cc: Steven Rostedt , Frederic Weisbecker , Pierre Tardy , Ingo Molnar , Arnaldo Carvalho de Melo , Tom Zanussi , Paul Mackerras , linux-kernel@vger.kernel.org, arjan@infradead.org, ziga.mahkovec@gmail.com, davem , linux-mm@kvack.org, Andrew Morton , KOSAKI Motohiro , Christoph Lameter , Tejun Heo , Jens Axboe List-ID: * Peter Zijlstra (peterz@infradead.org) wrote: > On Mon, 2010-05-17 at 18:42 -0400, Mathieu Desnoyers wrote: > > I'll continue to look into this. One of the things I noticed that that we could > > possibly use the "steal()" operation to steal the pages back from the page cache > > to repopulate the ring buffer rather than continuously allocating new pages. If > > steal() fails for some reasons, then we can fall back on page allocation. I'm > > not sure it is safe to assume anything about pages being in the page cache > > though. > > Also, suppose it was still in the page-cache and still dirty, a steal() > would then punch a hole in the file. page_cache_pipe_buf_steal starts by doing a wait_on_page_writeback(page); and then does a try_to_release_page(page, GFP_KERNEL). Only if that succeeds is the action of stealing succeeding. > > > Maybe the safest route is to just allocate new pages for now. > > Yes, that seems to be the only sane approach. Yes, a good start anyway. Thanks, Mathieu -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org