From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx205.postini.com [74.125.245.205]) by kanga.kvack.org (Postfix) with SMTP id E89146B0005 for ; Fri, 25 Jan 2013 05:14:53 -0500 (EST) Date: Fri, 25 Jan 2013 15:44:48 +0530 From: Amit Shah Subject: Re: [RFC 2/2] virtio_balloon: add auto-ballooning support Message-ID: <20130125101448.GG30483@amit.redhat.com> References: <1355861850-2702-1-git-send-email-lcapitulino@redhat.com> <1355861850-2702-3-git-send-email-lcapitulino@redhat.com> <20130111204317.GB11436@amit.redhat.com> <20130114100501.603ce8a4@doriath.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130114100501.603ce8a4@doriath.home> Sender: owner-linux-mm@kvack.org List-ID: To: Luiz Capitulino Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, riel@redhat.com, aquini@redhat.com, mst@redhat.com, agl@us.ibm.com On (Mon) 14 Jan 2013 [10:05:01], Luiz Capitulino wrote: > On Sat, 12 Jan 2013 02:13:17 +0530 > Amit Shah wrote: > > > On (Tue) 18 Dec 2012 [18:17:30], Luiz Capitulino wrote: > > > The auto-ballooning feature automatically performs balloon inflate or > > > deflate based on host and guest memory pressure. This can help to > > > avoid swapping or worse in both, host and guest. > > > > > > Auto-ballooning has a host and a guest part. The host performs > > > automatic inflate by requesting the guest to inflate its balloon > > > when the host is facing memory pressure. The guest performs > > > automatic deflate when it's facing memory pressure itself. It's > > > expected that auto-inflate and auto-deflate will balance each > > > other over time. > > > > > > This commit implements the guest side of auto-ballooning. > > > > > > To perform automatic deflate, the virtio_balloon driver registers > > > a shrinker callback, which will try to deflate the guest's balloon > > > on guest memory pressure just like if it were a cache. The shrinker > > > callback is only registered if the host supports the > > > VIRTIO_BALLOON_F_AUTO_BALLOON feature bit. > > > > I'm wondering if guest should auto-deflate even when the AUTO_BALLOON > > feature isn't supported by the host: if a guest is under pressure, > > there's no way for it to tell the host and wait for the host to > > deflate the balloon, so it may be beneficial to just go ahead and > > deflate the balloon for all hosts. > > I see two problems with this. First, this will automagically override > balloon changes done by the user; and second, if we don't have the > auto-inflate part and if the host starts facing memory pressure, VMs > may start getting OOM. Practically, though, at least for hosts and VMs managed by libvirt, guests will be confined by cgroups so they don't exceed some pre-defined quota. Guests should always be assumed to be malicious and / or greedy, so I'm certain all host mgmt software will have some checks in place. Amit -- 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