From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id B6C7A6B0093 for ; Mon, 18 Jan 2010 16:56:06 -0500 (EST) Subject: Re: [RFC][PATCH] PM: Force GFP_NOIO during suspend/resume (was: Re: [linux-pm] Memory allocations in .suspend became very unreliable) From: Benjamin Herrenschmidt In-Reply-To: <201001180000.23376.rjw@sisk.pl> References: <1263549544.3112.10.camel@maxim-laptop> <201001171427.27954.rjw@sisk.pl> <1263754684.724.444.camel@pasglop> <201001180000.23376.rjw@sisk.pl> Content-Type: text/plain; charset="UTF-8" Date: Tue, 19 Jan 2010 08:55:57 +1100 Message-ID: <1263851757.724.500.camel@pasglop> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: "Rafael J. Wysocki" Cc: Oliver Neukum , Maxim Levitsky , linux-pm@lists.linux-foundation.org, LKML , linux-mm , Andrew Morton List-ID: 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 ? :-) 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. Cheers, Ben. -- 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