From nobody Sun Nov 9 20:22:41 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1551762903257120.96455853059308; Mon, 4 Mar 2019 21:15:03 -0800 (PST) Received: from localhost ([127.0.0.1]:37593 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h12Pt-0003SE-8M for importer@patchew.org; Tue, 05 Mar 2019 00:15:01 -0500 Received: from eggs.gnu.org ([209.51.188.92]:54512) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h12Mh-0001Ch-Kj for qemu-devel@nongnu.org; Tue, 05 Mar 2019 00:11:44 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1h12Mg-0005pe-S1 for qemu-devel@nongnu.org; Tue, 05 Mar 2019 00:11:43 -0500 Received: from ozlabs.org ([2401:3900:2:1::2]:46527) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1h12Mg-0005n4-AC; Tue, 05 Mar 2019 00:11:42 -0500 Received: by ozlabs.org (Postfix, from userid 1007) id 44D4kL36N2z9s7T; Tue, 5 Mar 2019 16:11:38 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gibson.dropbear.id.au; s=201602; t=1551762698; bh=I+ybT0xcEk1EEZor34IilzQ9tq530tHRymLSQoAIItI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=a4HXPOPXGLyMVsw038sU3tB1BqccoShMaXRfhlLC1scXh0fGamwElqpY6CGTpqGpP blumdT5KiRsTng/zNhBhg2V/82JwS/bPctrT3MqueZdFBfjx9JPPa3ul42BQ1EXDkr WSsrdqwGGhtpzHuaSqdIGOBzb/3WZGDGPs+RuXVU= From: David Gibson To: mst@redhat.com, david@redhat.com Date: Tue, 5 Mar 2019 16:11:34 +1100 Message-Id: <20190305051134.27930-3-david@gibson.dropbear.id.au> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190305051134.27930-1-david@gibson.dropbear.id.au> References: <20190305051134.27930-1-david@gibson.dropbear.id.au> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2401:3900:2:1::2 Subject: [Qemu-devel] [RFC 2/2] virtio-balloon: Restore MADV_WILLNEED hint on balloon deflate X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-ppc@nongnu.org, qemu-devel@nongnu.org, David Gibson Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" Prior to f6deb6d9 "virtio-balloon: Remove unnecessary MADV_WILLNEED on deflate", the balloon device issued an madvise() MADV_WILLNEED on pages removed from the balloon. That would hint to the host kernel that the pages were likely to be needed by the guest in the near future. It's unclear if this is actually valuable or not, and so f6deb6d9 removed this, essentially ignoring balloon deflate requests. However, concerns have been raised that this might cause a performance regression by causing extra latency for the guest in certain configurations. So, until we can get actual benchmark data to see if that's the case, this restores (by default) the old behaviour, issuing a MADV_WILLNEED when a page is removed from the balloon. A new property on the balloon device "hint-on-deflate" can be set to false to remove this behaviour for testing. Signed-off-by: David Gibson --- hw/virtio/virtio-balloon.c | 15 +++++++++++++++ include/hw/virtio/virtio-balloon.h | 1 + 2 files changed, 16 insertions(+) diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c index e5e82b556d..69968502d9 100644 --- a/hw/virtio/virtio-balloon.c +++ b/hw/virtio/virtio-balloon.c @@ -146,6 +146,20 @@ static void balloon_deflate_page(VirtIOBalloon *balloo= n, balloon->pbp =3D NULL; } } + + if (balloon->hint_on_deflate) { + void *host_addr =3D (void *)((uintptr_t)addr & ~(rb_page_size - 1)= ); + int ret; + + /* When a page is deflated, we hint the whole host page it + * lives on, since we can't do anything smaller */ + ret =3D qemu_madvise(host_addr, rb_page_size, QEMU_MADV_WILLNEED); + if (ret !=3D 0) { + warn_report("Couldn't MADV_WILLNEED on balloon deflate: %s", + strerror(errno)); + /* Otherwise ignore, failing to page hint shouldn't be fatal */ + } + } } =20 static const char *balloon_stat_names[] =3D { @@ -622,6 +636,7 @@ static const VMStateDescription vmstate_virtio_balloon = =3D { static Property virtio_balloon_properties[] =3D { DEFINE_PROP_BIT("deflate-on-oom", VirtIOBalloon, host_features, VIRTIO_BALLOON_F_DEFLATE_ON_OOM, false), + DEFINE_PROP_BOOL("hint-on-deflate", VirtIOBalloon, hint_on_deflate, tr= ue), DEFINE_PROP_END_OF_LIST(), }; =20 diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-= balloon.h index 99dcd6d105..69732cedaa 100644 --- a/include/hw/virtio/virtio-balloon.h +++ b/include/hw/virtio/virtio-balloon.h @@ -45,6 +45,7 @@ typedef struct VirtIOBalloon { int64_t stats_poll_interval; uint32_t host_features; PartiallyBalloonedPage *pbp; + bool hint_on_deflate; } VirtIOBalloon; =20 #endif --=20 2.20.1