From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx113.postini.com [74.125.245.113]) by kanga.kvack.org (Postfix) with SMTP id E903D6B0006 for ; Fri, 18 Jan 2013 14:20:37 -0500 (EST) Message-ID: <1358536835.7383.31.camel@gandalf.local.home> Subject: Re: [RFC][PATCH v3] slub: Keep page and object in sync in slab_alloc_node() From: Steven Rostedt Date: Fri, 18 Jan 2013 14:20:35 -0500 In-Reply-To: <1358536190.11051.573.camel@edumazet-glaptop> References: <1358446258.23211.32.camel@gandalf.local.home> <1358447864.23211.34.camel@gandalf.local.home> <0000013c4a69a2cf-1a19a6f6-e6a3-4f06-99a4-10fdd4b9aca2-000000@email.amazonses.com> <1358458996.23211.46.camel@gandalf.local.home> <0000013c4a7e7fbf-c51fd42a-2455-4fec-bb37-915035956f05-000000@email.amazonses.com> <1358462763.23211.57.camel@gandalf.local.home> <1358464245.23211.62.camel@gandalf.local.home> <1358464837.23211.66.camel@gandalf.local.home> <1358468598.23211.67.camel@gandalf.local.home> <1358468924.23211.69.camel@gandalf.local.home> <1358521791.7383.11.camel@gandalf.local.home> <0000013c4ef61783-2778b0f1-fdc1-421b-9d3e-ccd68d528115-000000@email.amazonses.com> <1358536190.11051.573.camel@edumazet-glaptop> Content-Type: text/plain; charset="ISO-8859-15" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Eric Dumazet Cc: Christoph Lameter , LKML , linux-mm , Andrew Morton , Pekka Enberg , Matt Mackall , Thomas Gleixner , RT , Clark Williams , John Kacur , "Luis Claudio R. Goncalves" On Fri, 2013-01-18 at 11:09 -0800, Eric Dumazet wrote: > On Fri, 2013-01-18 at 18:40 +0000, Christoph Lameter wrote: > > > The fetching of the tid is the only critical thing here. If the tid is > > retrieved from the right cpu then the cmpxchg will fail if any changes > > occured to freelist or the page variable. > > > > The tid can be retrieved without disabling preemption through > > this_cpu_read(). > > Strictly speaking, this_cpu_read() _does_ disable preemption. I was thinking the same thing. > > Of course, on x86, this_cpu_read() uses __this_cpu_read() Looking at using this_cpu_read() on tid, I can't see what would break. We still need the check for page being NULL in node_match(). I'm still uneasy about it. Just because we can't see how it might break doesn't mean that it wont. As we have already found a bit of bugs in the current code. I'd feel more comfortable with the explicit preempt_disable(). And this is coming from an -rt guy that tries to avoid preempt_disable(). But you're (Christoph) the maintainer. I guess if you use this_cpu_read() you don't need that barrier anymore. -- Steve -- 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