Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933955Ab3HJOGS (ORCPT ); Sat, 10 Aug 2013 10:06:18 -0400 Received: from mail-wg0-f41.google.com ([74.125.82.41]:48979 "EHLO mail-wg0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755519Ab3HJOGR (ORCPT ); Sat, 10 Aug 2013 10:06:17 -0400 MIME-Version: 1.0 In-Reply-To: References: <1376037909-17797-1-git-send-email-namhyung@kernel.org> <1376037909-17797-11-git-send-email-namhyung@kernel.org> <5204BCE6.2070102@hitachi.com> <20130809162002.GA7144@redhat.com> Date: Sat, 10 Aug 2013 22:06:16 +0800 Message-ID: Subject: Re: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a ring buffer From: "zhangwei(Jovi)" To: Oleg Nesterov Cc: Masami Hiramatsu , Steven Rostedt , Namhyung Kim , Namhyung Kim , Hyeoncheol Lee , LKML , Srikar Dronamraju , "zhangwei(Jovi)" , Arnaldo Carvalho de Melo Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1917 Lines: 47 On Sat, Aug 10, 2013 at 9:41 AM, zhangwei(Jovi) wrote: > On Sat, Aug 10, 2013 at 9:26 AM, zhangwei(Jovi) wrote: >> On Sat, Aug 10, 2013 at 12:20 AM, Oleg Nesterov wrote: >>> >>> Sorry, I didn't read this series yet. Not that I think this needs my >>> help, but I'll try to do this a later... >>> >>> On 08/09, Masami Hiramatsu wrote: >>> > >>> > I just concern using kmalloc() in the event handler. >>> >>> GFP_KERNEL should be fine for uprobe handler. >>> >>> However, iirc this conflicts with the patches from Jovi, >>> "Support ftrace_event_file base multibuffer" adds rcu_read_lock() >>> around uprobe_trace_print(). >> >> (Sorry about html text rejected by kernel.org, send again with plain text.) >> >> Then we might need to call kmalloc before rcu_read_lock, also call kfree >> after rcu_read_unlock. >> >> And it's not needed to call kmalloc for each instances in multi-buffer >> case, just >> kmalloc once is enough. >> >> I also have same concern about use kmalloc in uprobe handler, use kmalloc >> in uprobe handler seems have a little overhead, why not pre-allocate one page >> static memory for temp buffer(perhaps trace_uprobe based)? one page size >> would be enough for all uprobe args storage, then we don't need to call >> kmalloc in that "fast path". >> > forgotten to say, that pre-allocated buffer would need to be per-cpu, to prevent > buffer corruption. > > It's a memory space vs. performance trade-off problem. :) > Oops, I missed the per-cpu buffer operation still need preempt_disable, ignore this part of my comments, now I agree kmalloc in uprobe handler is needed. jovi. -- 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/