From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932457AbaDBQgq (ORCPT ); Wed, 2 Apr 2014 12:36:46 -0400 Received: from zene.cmpxchg.org ([85.214.230.12]:58075 "EHLO zene.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932282AbaDBQgp (ORCPT ); Wed, 2 Apr 2014 12:36:45 -0400 Date: Wed, 2 Apr 2014 12:36:38 -0400 From: Johannes Weiner To: John Stultz Cc: Dave Hansen , "H. Peter Anvin" , LKML , Andrew Morton , Android Kernel Team , Robert Love , Mel Gorman , Hugh Dickins , Rik van Riel , Dmitry Adamushko , Neil Brown , Andrea Arcangeli , Mike Hommey , Taras Glek , Jan Kara , KOSAKI Motohiro , Michel Lespinasse , Minchan Kim , "linux-mm@kvack.org" Subject: Re: [PATCH 0/5] Volatile Ranges (v12) & LSF-MM discussion fodder Message-ID: <20140402163638.GQ14688@cmpxchg.org> References: <1395436655-21670-1-git-send-email-john.stultz@linaro.org> <20140401212102.GM4407@cmpxchg.org> <533B313E.5000403@zytor.com> <533B4555.3000608@sr71.net> <533B8E3C.3090606@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <533B8E3C.3090606@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 01, 2014 at 09:12:44PM -0700, John Stultz wrote: > On 04/01/2014 04:01 PM, Dave Hansen wrote: > > On 04/01/2014 02:35 PM, H. Peter Anvin wrote: > >> On 04/01/2014 02:21 PM, Johannes Weiner wrote: > >>> Either way, optimistic volatile pointers are nowhere near as > >>> transparent to the application as the above description suggests, > >>> which makes this usecase not very interesting, IMO. > >> ... however, I think you're still derating the value way too much. The > >> case of user space doing elastic memory management is more and more > >> common, and for a lot of those applications it is perfectly reasonable > >> to either not do system calls or to have to devolatilize first. > > The SIGBUS is only in cases where the memory is set as volatile and > > _then_ accessed, right? > Not just set volatile and then accessed, but when a volatile page has > been purged and then accessed without being made non-volatile. > > > > John, this was something that the Mozilla guys asked for, right? Any > > idea why this isn't ever a problem for them? > So one of their use cases for it is for library text. Basically they > want to decompress a compressed library file into memory. Then they plan > to mark the uncompressed pages volatile, and then be able to call into > it. Ideally for them, the kernel would only purge cold pages, leaving > the hot pages in memory. When they traverse a purged page, they handle > the SIGBUS and patch the page up. How big are these libraries compared to overall system size? > Now.. this is not what I'd consider a normal use case, but was hoping to > illustrate some of the more interesting uses and demonstrate the > interfaces flexibility. I'm just dying to hear a "normal" use case then. :) > Also it provided a clear example of benefits to doing LRU based > cold-page purging rather then full object purging. Though I think the > same could be demonstrated in a simpler case of a large cache of objects > that the applications wants to mark volatile in one pass, unmarking > sub-objects as it needs. Agreed.