From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43656) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WGpeg-0007pn-Dy for qemu-devel@nongnu.org; Fri, 21 Feb 2014 07:56:44 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WGpea-0003TQ-8y for qemu-devel@nongnu.org; Fri, 21 Feb 2014 07:56:38 -0500 Received: from mail-pd0-f174.google.com ([209.85.192.174]:60148) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WGpea-0003Sm-35 for qemu-devel@nongnu.org; Fri, 21 Feb 2014 07:56:32 -0500 Received: by mail-pd0-f174.google.com with SMTP id z10so3239275pdj.19 for ; Fri, 21 Feb 2014 04:56:29 -0800 (PST) Message-ID: <53074CF8.4090900@ozlabs.ru> Date: Fri, 21 Feb 2014 23:56:24 +1100 From: Alexey Kardashevskiy MIME-Version: 1.0 References: <1392013975-1656-1-git-send-email-aik@ozlabs.ru> <5306DCC0.7010107@ozlabs.ru> <1A5B5EFA-FE6C-46F6-BA22-D524B6F43207@suse.de> In-Reply-To: <1A5B5EFA-FE6C-46F6-BA22-D524B6F43207@suse.de> Content-Type: text/plain; charset=KOI8-R Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC PATCH] file ram alloc: fail if cannot preallocate List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexander Graf Cc: Antonios Motakis , "list@suse.de:PowerPC" , QEMU Developers , Paolo Bonzini On 02/21/2014 07:57 PM, Alexander Graf wrote: > > On 21.02.2014, at 05:57, Alexey Kardashevskiy wrote: > >> On 02/10/2014 05:32 PM, Alexey Kardashevskiy wrote: >>> At the moment if the user asked for huge pages and there is no more huge >>> pages, QEMU prints warning and falls back to the anonymous memory >>> allocator which is quite easy not to notice. QEMU also does so even >>> if the user specified -mem-prealloc and it seems wrong as the user >>> specifically requested huge pages for the entire RAM but QEMU failed to do >>> so and continued. On PPC64 this will produce a fragile guest as QEMU >>> tells the guest via device-tree that it can use huge pages when it >>> actually cannot. >>> >>> This adds message+exit if RAM cannot be preallocated from huge pages. >> >> >> Too bad? Should I increase my personal pinging timeout from 1 to 2 weeks to >> avoid annoying the community? :) Thanks! > > The patch changes the semantics of -mem-prealloc from "make sure all > RAM is mapped" to "make sure all RAM is mapped and is backed by huge > pages if we use huge pages" and thus is just plain wrong. ? I did actually expect it to alloc RAM from hugepages only. Otherwise there is no point in mem-prealloc. Yes, I am ignorant, I know. > The real question is why are we allowing sparsely mapped huge page backing at all? Should we change that? Do we need a new flag for this to specify "yes, I do want all my pages backed by -mem-path"? ? Add a switch to -mem-path saying "yes I really want -mem-path"? Sorry, I lost you here. -mem-path + -mem-prealloc - like this is not enough? Why would I specify -mem-path after all if I did not want RAM to backed by huge pages? > This is also something that should be coordinated with the -mem-path refactoring. Oh. There is always refactoring :( -- Alexey