From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx149.postini.com [74.125.245.149]) by kanga.kvack.org (Postfix) with SMTP id 8E1296B004A for ; Tue, 17 Apr 2012 13:11:04 -0400 (EDT) Date: Tue, 17 Apr 2012 19:09:58 +0200 From: Oleg Nesterov Subject: Re: [PATCH 2/6] uprobes: introduce is_swbp_at_addr_fast() Message-ID: <20120417170958.GA16511@redhat.com> References: <20120405222024.GA19154@redhat.com> <20120405222106.GB19166@redhat.com> <1334570935.28150.25.camel@twins> <20120416144457.GA7018@redhat.com> <1334588109.28150.59.camel@twins> <20120416153408.GA8852@redhat.com> <1334657287.28150.77.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1334657287.28150.77.camel@twins> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra 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 04/17, Peter Zijlstra wrote: > > On Mon, 2012-04-16 at 17:34 +0200, Oleg Nesterov wrote: > > On 04/16, Peter Zijlstra wrote: > > > > > > Can't we 'optimize' read_opcode() by doing the pagefault_disable() + > > > __copy_from_user_inatomic() optimistically before going down the whole > > > gup()+lock+kmap path? > > > > Unlikely, the task is not current. > > Easy enough to test that though.. and that should make the regular path > fast enough, no? > > > --- > kernel/events/uprobes.c | 9 +++++++++ > 1 files changed, 9 insertions(+), 0 deletions(-) > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > index 985be4d..7f5d8c5 100644 > --- a/kernel/events/uprobes.c > +++ b/kernel/events/uprobes.c > @@ -312,6 +312,15 @@ static int read_opcode(struct mm_struct *mm, unsigned long vaddr, uprobe_opcode_ > void *vaddr_new; > int ret; > > + if (mm == current->mm) { > + pagefault_disable(); > + ret = __copy_from_user_inatomic(opcode, (void __user *)vaddr, > + sizeof(*opcode)); > + pagefault_enable(); > + if (!ret) > + return 0; > + } Indeed. And then we do not need is_swbp_at_addr_fast(). This reminds me. Why read_opcode() does lock_page? I was going to send the cleanup which removes it, but I need to recheck. Perhaps you can explain the reason? Oleg. -- 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