From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 73E736B0078 for ; Wed, 20 Jan 2010 16:20:56 -0500 (EST) From: "Rafael J. Wysocki" Subject: Re: [RFC][PATCH] PM: Force GFP_NOIO during suspend/resume (was: Re: [linux-pm] Memory allocations in .suspend became very unreliable) Date: Wed, 20 Jan 2010 22:21:34 +0100 References: <1263871194.724.520.camel@pasglop> <201001192147.58185.rjw@sisk.pl> <20100120085053.405A.A69D9226@jp.fujitsu.com> In-Reply-To: <20100120085053.405A.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <201001202221.34804.rjw@sisk.pl> Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: Benjamin Herrenschmidt , Maxim Levitsky , linux-pm@lists.linux-foundation.org, LKML , linux-mm , Andrew Morton List-ID: On Wednesday 20 January 2010, KOSAKI Motohiro wrote: > > On Tuesday 19 January 2010, Benjamin Herrenschmidt wrote: > > > On Tue, 2010-01-19 at 10:19 +0900, KOSAKI Motohiro wrote: > > > > I think the race happen itself is bad. memory and I/O subsystem can't solve such race > > > > elegantly. These doesn't know enough suspend state knowlege. I think the practical > > > > solution is that higher level design prevent the race happen. > > > > > > > > > > > > > My patch attempts to avoid these two problems as well as the problem with > > > > > drivers using GFP_KERNEL allocations during suspend which I admit might be > > > > > solved by reworking the drivers. > > > > > > > > Agreed. In this case, only drivers change can solve the issue. > > > > > > As I explained earlier, this is near to impossible since the allocations > > > are too often burried deep down the call stack or simply because the > > > driver doesn't know that we started suspending -another- driver... > > > > > > I don't think trying to solve those problems at the driver level is > > > realistic to be honest. This is one of those things where we really just > > > need to make allocators 'just work' from a driver perspective. > > > > > > It can't be perfect of course, as mentioned earlier, there will be a > > > problem if too little free memory is really available due to lots of > > > dirty pages around, but most of this can be somewhat alleviated in > > > practice, for example by pushing things out a bit at suspend time, > > > making some more memory free etc... But yeah, nothing replaces proper > > > error handling in drivers for allocation failures even with > > > GFP_KERNEL :-) > > > > Agreed. > > > > Moreover, I didn't try to do anything about that before, because memory > > allocation problems during suspend/resume just didn't happen. We kind of knew > > they were possible, but since they didn't show up, it wasn't immediately > > necessary to address them. > > > > Now, however, people started to see these problems in testing and I'm quite > > confident that this is a result of recent changes in the mm subsystem. Namely, > > if you read the Maxim's report carefully, you'll notice that in his test case > > the mm subsystem apparently attempted to use I/O even though there was free > > memory available in the system. This is the case I want to prevent from > > happening in the first place. > > Hi Rafael, > > Do you mean this is the unrelated issue of nVidia bug? The nvidia driver _is_ buggy, but Maxim said he couldn't reproduce the problem if all the allocations made by the nvidia driver during suspend were changed to GFP_ATOMIC. > Probably I haven't catch your point. I don't find Maxim's original bug > report. Can we share the test-case and your analysis detail? The Maxim's original report is here: https://lists.linux-foundation.org/pipermail/linux-pm/2010-January/023982.html and the message I'm referring to is at: https://lists.linux-foundation.org/pipermail/linux-pm/2010-January/023990.html Thanks, Rafael -- 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