From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 5FA0D600473 for ; Mon, 18 Jan 2010 18:33:06 -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: Tue, 19 Jan 2010 00:33:15 +0100 References: <1263549544.3112.10.camel@maxim-laptop> <201001180000.23376.rjw@sisk.pl> <1263851757.724.500.camel@pasglop> In-Reply-To: <1263851757.724.500.camel@pasglop> MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <201001190033.16055.rjw@sisk.pl> Sender: owner-linux-mm@kvack.org To: Benjamin Herrenschmidt Cc: Oliver Neukum , Maxim Levitsky , linux-pm@lists.linux-foundation.org, LKML , linux-mm , Andrew Morton List-ID: On Monday 18 January 2010, Benjamin Herrenschmidt wrote: > On Mon, 2010-01-18 at 00:00 +0100, Rafael J. Wysocki wrote: > > On Sunday 17 January 2010, Benjamin Herrenschmidt wrote: > > > On Sun, 2010-01-17 at 14:27 +0100, Rafael J. Wysocki wrote: > > ... > > > However, it's hard to deal with the case of allocations that have > > > already started waiting for IOs. It might be possible to have some VM > > > hook to make them wakeup, re-evaluate the situation and get out of that > > > code path but in any case it would be tricky. > > > > In the second version of the patch I used an rwsem that made us wait for these > > allocations to complete before we changed gfp_allowed_mask. > > > > [This is kinda buggy in the version I sent, but I'm going to send an update > > in a minute.] > > And nobody screamed due to cache line ping pong caused by this in the > fast path ? :-) Apparently not. :-) > We might want to look at something a bit smarter for that sort of > read-mostly-really-really-mostly construct, though in this case I don't > think RCU is the answer since we are happily scheduling. > > I wonder if something per-cpu would do, it's thus the responsibility of > the "writer" to take them all in order for all CPUs. I think I'll get back to the first version of the patch which I think is not going to have side effects (as long as no one will change gfp_allowed_mask in parallel with suspend/resume), for now. We can add more complicated things on top of it, then. 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