Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755284Ab2HNTvf (ORCPT ); Tue, 14 Aug 2012 15:51:35 -0400 Received: from mx1.redhat.com ([209.132.183.28]:12959 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752041Ab2HNTvd (ORCPT ); Tue, 14 Aug 2012 15:51:33 -0400 Date: Tue, 14 Aug 2012 22:52:27 +0300 From: "Michael S. Tsirkin" To: Rafael Aquini Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Rusty Russell , Rik van Riel , Mel Gorman , Andi Kleen , Andrew Morton , Konrad Rzeszutek Wilk , Minchan Kim Subject: Re: [PATCH v7 1/4] mm: introduce compaction and migration for virtio ballooned pages Message-ID: <20120814195227.GB28870@redhat.com> References: <292b1b52e863a05b299f94bda69a61371011ac19.1344619987.git.aquini@redhat.com> <20120813082619.GE14081@redhat.com> <20120814174404.GA13338@t510.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120814174404.GA13338@t510.redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2159 Lines: 53 On Tue, Aug 14, 2012 at 02:44:05PM -0300, Rafael Aquini wrote: > On Mon, Aug 13, 2012 at 11:26:19AM +0300, Michael S. Tsirkin wrote: > > > +static inline bool movable_balloon_page(struct page *page) > > > +{ > > > + return (page->mapping && page->mapping == balloon_mapping); > > > > I am guessing this needs smp_read_barrier_depends, and maybe > > ACCESS_ONCE ... > > > > I'm curious about your guessing here. Could you ellaborate it further, please? well balloon_mapping can change dynamically. I think actually rcu is a good fit here. > > > > +#else > > > +static inline bool isolate_balloon_page(struct page *page) { return false; } > > > +static inline void putback_balloon_page(struct page *page) { return false; } > > > +static inline bool movable_balloon_page(struct page *page) { return false; } > > > +#endif /* (VIRTIO_BALLOON || VIRTIO_BALLOON_MODULE) && CONFIG_COMPACTION */ > > > + > > > > This does mean that only one type of balloon is useable at a time. > > I wonder whether using a flag in address_space structure instead > > is possible ... > > This means we are only introducing this feature for virtio_balloon by now. > Despite the flagging address_space stuff is something we surely can look in the > future, I quite didn't get how we could be using two different types of balloon > devices at the same time for the same system. Could you ellaborate it a little > more, please? > > > > > +/* __isolate_lru_page() counterpart for a ballooned page */ > > > +bool isolate_balloon_page(struct page *page) > > > +{ > > > + if (WARN_ON(!movable_balloon_page(page))) > > > > Looks like this actually can happen if the page is leaked > > between previous movable_balloon_page and here. > > > > > + return false; > > Yes, it surely can happen, and it does not harm to catch it here, print a warn and > return. While testing it, I wasn't lucky to see this small window opening, though. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/