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 SMTP id 081496B004D for ; Fri, 13 Nov 2009 00:08:04 -0500 (EST) Date: Thu, 12 Nov 2009 13:33:39 +0100 From: Pavel Machek Subject: using highmem for atomic copy of lowmem was Re: [PATCHv2 2/5] vmscan: Kill hibernation specific reclaim logic and unify it Message-ID: <20091112123339.GA1546@ucw.cz> References: <20091102000855.F404.A69D9226@jp.fujitsu.com> <200911031230.20344.rjw@sisk.pl> <4AF09CB2.9030500@crca.org.au> <200911032300.14790.rjw@sisk.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200911032300.14790.rjw@sisk.pl> Sender: owner-linux-mm@kvack.org To: "Rafael J. Wysocki" Cc: Nigel Cunningham , KOSAKI Motohiro , LKML , Rik van Riel , linux-mm , Andrew Morton List-ID: Hi! > > >> (Disclaimer: I don't think about highmem a lot any more, and might have > > >> forgotten some of the details, or swsusp's algorithms might have > > >> changed. Rafael might need to correct some of this...) > > >> > > >> Imagine that you have a system with 1000 pages of lowmem and 5000 pages > > >> of highmem. Of these, 950 lowmem pages are in use and 500 highmem pages > > >> are in use. > > >> > > >> In order to to be able to save an image, we need to be able to do an > > >> atomic copy of those lowmem pages. > > >> > > >> You might think that we could just copy everything into the spare > > >> highmem pages, but we can't because mapping and unmapping the highmem > > >> pages as we copy the data will leave us with an inconsistent copy. > > > > > > This isn't the case any more for the mainline hibernate code. We use highmem > > > for storing image data as well as lowmem. > > > > Highmem for storing copies of lowmem pages? > > It is possible in theory, but I don't think it happens in practice given the > way in which the memory is freed. Still copy_data_page() takes this > possibility into account. Yes, it does, but I wonder if it can ever work...? copy_data_page() takes great care not to modify any memory -- like using handmade loop instead of memcpy() -- yet it uses kmap_atomic() and friends. If kmap_atomic()+kunmap_atomic() pair is guaranteed not to change any memory, thats probably safe, but... (Actually, plain memcpy() should be usable for copying highmem pages; those should not contain task_structs or anything else touched by memcpy()). Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- 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