From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Williamson Subject: Re: [RFC PATCH 1/3] balloon: Allow nested inhibits Date: Wed, 18 Jul 2018 10:37:36 -0600 Message-ID: <20180718103736.2406cdc8@t450s.home> References: <20180717222721.14019.27548.stgit@gimli.home> <20180717224737.14019.3324.stgit@gimli.home> <20180718064015.GI20520@xz-mi> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org To: Peter Xu Return-path: In-Reply-To: <20180718064015.GI20520@xz-mi> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel2=m.gmane.org@nongnu.org Sender: "Qemu-devel" List-Id: kvm.vger.kernel.org On Wed, 18 Jul 2018 14:40:15 +0800 Peter Xu wrote: > On Tue, Jul 17, 2018 at 04:47:37PM -0600, Alex Williamson wrote: > > A simple true/false internal state does not allow multiple users. Fix > > this within the existing interface by converting to a counter, so long > > as the counter is elevated, ballooning is inhibited. > > > > Signed-off-by: Alex Williamson > > --- > > balloon.c | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > diff --git a/balloon.c b/balloon.c > > index 6bf0a9681377..2a6a7e1a22a0 100644 > > --- a/balloon.c > > +++ b/balloon.c > > @@ -37,16 +37,17 @@ > > static QEMUBalloonEvent *balloon_event_fn; > > static QEMUBalloonStatus *balloon_stat_fn; > > static void *balloon_opaque; > > -static bool balloon_inhibited; > > +static int balloon_inhibited; > > > > bool qemu_balloon_is_inhibited(void) > > { > > - return balloon_inhibited; > > + return balloon_inhibited > 0; > > } > > > > void qemu_balloon_inhibit(bool state) > > { > > - balloon_inhibited = state; > > + balloon_inhibited += (state ? 1 : -1); > > + assert(balloon_inhibited >= 0); > > Better do it atomically? I'd assumed we're protected by the BQL anywhere this is called. Is that not the case? Generally when I try to add any sort of locking to QEMU it's shot down because the code paths are already serialized. Thanks, Alex