From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754318Ab2DTKO1 (ORCPT ); Fri, 20 Apr 2012 06:14:27 -0400 Received: from merlin.infradead.org ([205.233.59.134]:53499 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753318Ab2DTKO0 (ORCPT ); Fri, 20 Apr 2012 06:14:26 -0400 Subject: Re: [RFC 0/6] uprobes: kill uprobes_srcu/uprobe_srcu_id From: Peter Zijlstra To: Oleg Nesterov Cc: Ingo Molnar , Srikar Dronamraju , Andrew Morton , Linus Torvalds , Ananth N Mavinakayanahalli , Jim Keniston , LKML , Linux-mm , Andi Kleen , Christoph Hellwig , Steven Rostedt , Arnaldo Carvalho de Melo , Masami Hiramatsu , Thomas Gleixner , Anton Arapov In-Reply-To: <20120416214707.GA27639@redhat.com> References: <20120405222024.GA19154@redhat.com> <1334409396.2528.100.camel@twins> <20120414205200.GA9083@redhat.com> <1334487062.2528.113.camel@twins> <20120415195351.GA22095@redhat.com> <1334526513.28150.23.camel@twins> <20120415234401.GA32662@redhat.com> <1334571419.28150.30.camel@twins> <20120416214707.GA27639@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Fri, 20 Apr 2012 12:14:21 +0200 Message-ID: <1334916861.2463.50.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.32.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2012-04-16 at 23:47 +0200, Oleg Nesterov wrote: > On 04/16, Peter Zijlstra wrote: > > > > On Mon, 2012-04-16 at 01:44 +0200, Oleg Nesterov wrote: > > > > > And. I have another reason for down_write() in register/unregister. > > > I am still not sure this is possible (I had no time to try to > > > implement), but it seems to me we can kill the uprobe counter in > > > mm_struct. > > > > You mean by making register/unregister down_write, you're exclusive with > > munmap() > > .. and with register/unregister. > > Why do we need mm->uprobes_state.count? It is writeonly, except we > check it in the DIE_INT3 notifier before anything else to avoid the > unnecessary uprobes overhead. and uprobe_munmap(). > Suppose we kill it, and add the new MMF_HAS_UPROBE flag instead. > install_breakpoint() sets it unconditionally, > uprobe_pre_sstep_notifier() checks it. Argh, why are MMF_flags part of sched.h.. one would expect those to be in mm.h or mm_types.h.. somewhere near struct mm. > (And perhaps we can stop right here? I mean how often this can > slow down the debugger which installs int3 in the same mm?) > > Now we need to clear MMF_HAS_UPROBE somehowe, when the last > uprobe goes away. Lets ignore uprobe_map/unmap for simplicity. > > - We add another flag, MMF_UPROBE_RECALC, it is set by > remove_breakpoint(). > > - We change handle_swbp(). Ignoring all details it does: > > if (find_uprobe(vaddr)) > process_uprobe(); > else if (test_bit(MMF_HAS_UPROBE) && test_bit(MMF_UPROBE_RECALC)) > recalc_mmf_uprobe_flag(); > > where recalc_mmf_uprobe_flag() checks all vmas and either > clears both flags or MMF_UPROBE_RECALC only. > > This is the really slow O(n) path, but it can only happen after > unregister, and only if we hit another non-uprobe breakpoint > in the same mm. > > Something like this. What do you think? I think I can live with the simple set MMF_HAS_UPROBE and leave it at that. The better optimization seems to be to not install breakpoints when ->filter() excludes the task.. It looks like we currently install the breakpoint unconditionally and only ->filter() once we hit the breakpoint, which is somewhat sub-optimal. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx133.postini.com [74.125.245.133]) by kanga.kvack.org (Postfix) with SMTP id 0D01B6B004D for ; Fri, 20 Apr 2012 06:14:25 -0400 (EDT) Received: from dhcp-089-099-019-018.chello.nl ([89.99.19.18] helo=dyad.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.76 #1 (Red Hat Linux)) id 1SLArA-0000Wi-8Q for linux-mm@kvack.org; Fri, 20 Apr 2012 10:14:24 +0000 Subject: Re: [RFC 0/6] uprobes: kill uprobes_srcu/uprobe_srcu_id From: Peter Zijlstra In-Reply-To: <20120416214707.GA27639@redhat.com> References: <20120405222024.GA19154@redhat.com> <1334409396.2528.100.camel@twins> <20120414205200.GA9083@redhat.com> <1334487062.2528.113.camel@twins> <20120415195351.GA22095@redhat.com> <1334526513.28150.23.camel@twins> <20120415234401.GA32662@redhat.com> <1334571419.28150.30.camel@twins> <20120416214707.GA27639@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Fri, 20 Apr 2012 12:14:21 +0200 Message-ID: <1334916861.2463.50.camel@laptop> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Oleg Nesterov Cc: Ingo Molnar , Srikar Dronamraju , Andrew Morton , Linus Torvalds , Ananth N Mavinakayanahalli , Jim Keniston , LKML , Linux-mm , Andi Kleen , Christoph Hellwig , Steven Rostedt , Arnaldo Carvalho de Melo , Masami Hiramatsu , Thomas Gleixner , Anton Arapov On Mon, 2012-04-16 at 23:47 +0200, Oleg Nesterov wrote: > On 04/16, Peter Zijlstra wrote: > > > > On Mon, 2012-04-16 at 01:44 +0200, Oleg Nesterov wrote: > > > > > And. I have another reason for down_write() in register/unregister. > > > I am still not sure this is possible (I had no time to try to > > > implement), but it seems to me we can kill the uprobe counter in > > > mm_struct. > > > > You mean by making register/unregister down_write, you're exclusive with > > munmap() > > .. and with register/unregister. > > Why do we need mm->uprobes_state.count? It is writeonly, except we > check it in the DIE_INT3 notifier before anything else to avoid the > unnecessary uprobes overhead. and uprobe_munmap(). > Suppose we kill it, and add the new MMF_HAS_UPROBE flag instead. > install_breakpoint() sets it unconditionally, > uprobe_pre_sstep_notifier() checks it. Argh, why are MMF_flags part of sched.h.. one would expect those to be in mm.h or mm_types.h.. somewhere near struct mm. > (And perhaps we can stop right here? I mean how often this can > slow down the debugger which installs int3 in the same mm?) > > Now we need to clear MMF_HAS_UPROBE somehowe, when the last > uprobe goes away. Lets ignore uprobe_map/unmap for simplicity. > > - We add another flag, MMF_UPROBE_RECALC, it is set by > remove_breakpoint(). > > - We change handle_swbp(). Ignoring all details it does: > > if (find_uprobe(vaddr)) > process_uprobe(); > else if (test_bit(MMF_HAS_UPROBE) && test_bit(MMF_UPROBE_RECALC)) > recalc_mmf_uprobe_flag(); > > where recalc_mmf_uprobe_flag() checks all vmas and either > clears both flags or MMF_UPROBE_RECALC only. > > This is the really slow O(n) path, but it can only happen after > unregister, and only if we hit another non-uprobe breakpoint > in the same mm. > > Something like this. What do you think? I think I can live with the simple set MMF_HAS_UPROBE and leave it at that. The better optimization seems to be to not install breakpoints when ->filter() excludes the task.. It looks like we currently install the breakpoint unconditionally and only ->filter() once we hit the breakpoint, which is somewhat sub-optimal. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org