From patchwork Mon Jan 27 08:18:08 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 11352197 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id F1A11159A for ; Mon, 27 Jan 2020 08:21:01 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id CDD912168B for ; Mon, 27 Jan 2020 08:21:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b="C1irDws5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CDD912168B Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=amazon.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1ivzbv-0001Xk-HP; Mon, 27 Jan 2020 08:19:07 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1ivzbu-0001XT-8d for xen-devel@lists.xenproject.org; Mon, 27 Jan 2020 08:19:06 +0000 X-Inumbo-ID: ae3d2bde-40dd-11ea-84ee-12813bfff9fa Received: from smtp-fw-33001.amazon.com (unknown [207.171.190.10]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id ae3d2bde-40dd-11ea-84ee-12813bfff9fa; Mon, 27 Jan 2020 08:19:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1580113145; x=1611649145; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=AlgYXHZVMr+gkDp34KurcKlh0X9TRVaRFfmS+SsrAhM=; b=C1irDws5oV09JZu3Z4+RnpzDvptNqC3q5AsPRJfnXLmfWm85gqM1OS3x p8kvT/KlSNrH4sWqJi6dZoaROGB2XLl1uxpD86SudngKcnmK4L2LuDNI7 XGGQ4LW7Lg2cDvIlocCKb/GRd/ezUe3idtJo8RmeTewzYPsm4YpECXiW+ U=; IronPort-SDR: uMkQlNiB9w5LHs1zA7FOvJdLJiQC00IV2UorSjll8vNCEJaZKnmwAqbu3FMlvy4oKtfAHCugov 90/hYLNt0awA== X-IronPort-AV: E=Sophos;i="5.70,369,1574121600"; d="scan'208";a="22599795" Received: from sea32-co-svc-lb4-vlan3.sea.corp.amazon.com (HELO email-inbound-relay-2c-397e131e.us-west-2.amazon.com) ([10.47.23.38]) by smtp-border-fw-out-33001.sea14.amazon.com with ESMTP; 27 Jan 2020 08:18:43 +0000 Received: from EX13MTAUEA002.ant.amazon.com (pdx4-ws-svc-p6-lb7-vlan3.pdx.amazon.com [10.170.41.166]) by email-inbound-relay-2c-397e131e.us-west-2.amazon.com (Postfix) with ESMTPS id BBF46A22CE; Mon, 27 Jan 2020 08:18:42 +0000 (UTC) Received: from EX13D31EUA001.ant.amazon.com (10.43.165.15) by EX13MTAUEA002.ant.amazon.com (10.43.61.77) with Microsoft SMTP Server (TLS) id 15.0.1236.3; Mon, 27 Jan 2020 08:18:42 +0000 Received: from u886c93fd17d25d.ant.amazon.com (10.43.160.8) by EX13D31EUA001.ant.amazon.com (10.43.165.15) with Microsoft SMTP Server (TLS) id 15.0.1367.3; Mon, 27 Jan 2020 08:18:37 +0000 From: To: , , Date: Mon, 27 Jan 2020 09:18:08 +0100 Message-ID: <20200127081812.21216-2-sjpark@amazon.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200127081812.21216-1-sjpark@amazon.com> References: <20200127081812.21216-1-sjpark@amazon.com> MIME-Version: 1.0 X-Originating-IP: [10.43.160.8] X-ClientProxiedBy: EX13D11UWB004.ant.amazon.com (10.43.161.90) To EX13D31EUA001.ant.amazon.com (10.43.165.15) Precedence: Bulk Subject: [Xen-devel] [PATCH v14 1/5] xenbus/backend: Add memory pressure handler callback X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: konrad.wilk@oracle.com, pdurrant@amazon.com, SeongJae Park , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, xen-devel@lists.xenproject.org Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" From: SeongJae Park Granting pages consumes backend system memory. In systems configured with insufficient spare memory for those pages, it can cause a memory pressure situation. However, finding the optimal amount of the spare memory is challenging for large systems having dynamic resource utilization patterns. Also, such a static configuration might lack flexibility. To mitigate such problems, this commit adds a memory reclaim callback to 'xenbus_driver'. If a memory pressure is detected, 'xenbus' requests every backend driver to volunarily release its memory. Note that it would be able to improve the callback facility for more sophisticated handlings of general pressures. For example, it would be possible to monitor the memory consumption of each device and issue the release requests to only devices which causing the pressure. Also, the callback could be extended to handle not only memory, but general resources. Nevertheless, this version of the implementation defers such sophisticated goals as a future work. Reviewed-by: Juergen Gross Reviewed-by: Roger Pau Monné Signed-off-by: SeongJae Park --- drivers/xen/xenbus/xenbus_probe_backend.c | 32 +++++++++++++++++++++++ include/xen/xenbus.h | 1 + 2 files changed, 33 insertions(+) diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c index 14876faff3b0..3b5cb7a5a7e4 100644 --- a/drivers/xen/xenbus/xenbus_probe_backend.c +++ b/drivers/xen/xenbus/xenbus_probe_backend.c @@ -247,6 +247,35 @@ static int backend_probe_and_watch(struct notifier_block *notifier, return NOTIFY_DONE; } +static int backend_reclaim_memory(struct device *dev, void *data) +{ + const struct xenbus_driver *drv; + + if (!dev->driver) + return 0; + drv = to_xenbus_driver(dev->driver); + if (drv && drv->reclaim_memory) + drv->reclaim_memory(to_xenbus_device(dev)); + return 0; +} + +/* + * Returns 0 always because we are using shrinker to only detect memory + * pressure. + */ +static unsigned long backend_shrink_memory_count(struct shrinker *shrinker, + struct shrink_control *sc) +{ + bus_for_each_dev(&xenbus_backend.bus, NULL, NULL, + backend_reclaim_memory); + return 0; +} + +static struct shrinker backend_memory_shrinker = { + .count_objects = backend_shrink_memory_count, + .seeks = DEFAULT_SEEKS, +}; + static int __init xenbus_probe_backend_init(void) { static struct notifier_block xenstore_notifier = { @@ -263,6 +292,9 @@ static int __init xenbus_probe_backend_init(void) register_xenstore_notifier(&xenstore_notifier); + if (register_shrinker(&backend_memory_shrinker)) + pr_warn("shrinker registration failed\n"); + return 0; } subsys_initcall(xenbus_probe_backend_init); diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h index 24228a102141..980952ea452b 100644 --- a/include/xen/xenbus.h +++ b/include/xen/xenbus.h @@ -105,6 +105,7 @@ struct xenbus_driver { struct device_driver driver; int (*read_otherend_details)(struct xenbus_device *dev); int (*is_ready)(struct xenbus_device *dev); + void (*reclaim_memory)(struct xenbus_device *dev); }; static inline struct xenbus_driver *to_xenbus_driver(struct device_driver *drv) From patchwork Mon Jan 27 08:18:09 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 11352191 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id A34A4159A for ; Mon, 27 Jan 2020 08:20:05 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 7DC2C21569 for ; Mon, 27 Jan 2020 08:20:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b="n47aNtE0" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7DC2C21569 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=amazon.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1ivzbt-0001Wy-6r; Mon, 27 Jan 2020 08:19:05 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1ivzbs-0001Wl-Be for xen-devel@lists.xenproject.org; Mon, 27 Jan 2020 08:19:04 +0000 X-Inumbo-ID: a831641c-40dd-11ea-9fd7-bc764e2007e4 Received: from smtp-fw-33001.amazon.com (unknown [207.171.190.10]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id a831641c-40dd-11ea-9fd7-bc764e2007e4; Mon, 27 Jan 2020 08:18:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1580113135; x=1611649135; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version; bh=dm2qM4W8b5BZdLKOsyrt63daqngTk+Y1qGr35fS4OsQ=; b=n47aNtE0sEzuKZu27e1FUP8uKAakIVtLITnhaWIHHJqhUyWG6mGy9iqX kXNyPQTdeiiqnVWNYzKPvBXZFQxnwAPmvjL7spOk7lVLYZiz1F6UdQtbm K7mmD0/Zj5Xe6O8sBRUa5txQP73FXNAHV+qEXXQK1o+Ft+592LA41DSXe E=; IronPort-SDR: 8RkC+dRPpNCwzT4oTt6mIf+gDHsQWjpSZz9W0iuH2mB9IduHH3/j/VwwIVPHBKf6fOA/8AKhxt kPzbR7pnDsHQ== X-IronPort-AV: E=Sophos;i="5.70,369,1574121600"; d="scan'208";a="22599829" Received: from sea32-co-svc-lb4-vlan3.sea.corp.amazon.com (HELO email-inbound-relay-2b-baacba05.us-west-2.amazon.com) ([10.47.23.38]) by smtp-border-fw-out-33001.sea14.amazon.com with ESMTP; 27 Jan 2020 08:18:47 +0000 Received: from EX13MTAUEA002.ant.amazon.com (pdx4-ws-svc-p6-lb7-vlan2.pdx.amazon.com [10.170.41.162]) by email-inbound-relay-2b-baacba05.us-west-2.amazon.com (Postfix) with ESMTPS id BD122A2750; Mon, 27 Jan 2020 08:18:46 +0000 (UTC) Received: from EX13D31EUA001.ant.amazon.com (10.43.165.15) by EX13MTAUEA002.ant.amazon.com (10.43.61.77) with Microsoft SMTP Server (TLS) id 15.0.1236.3; Mon, 27 Jan 2020 08:18:46 +0000 Received: from u886c93fd17d25d.ant.amazon.com (10.43.160.8) by EX13D31EUA001.ant.amazon.com (10.43.165.15) with Microsoft SMTP Server (TLS) id 15.0.1367.3; Mon, 27 Jan 2020 08:18:41 +0000 From: To: , , Date: Mon, 27 Jan 2020 09:18:09 +0100 Message-ID: <20200127081812.21216-3-sjpark@amazon.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200127081812.21216-1-sjpark@amazon.com> References: <20200127081812.21216-1-sjpark@amazon.com> MIME-Version: 1.0 X-Originating-IP: [10.43.160.8] X-ClientProxiedBy: EX13D11UWB004.ant.amazon.com (10.43.161.90) To EX13D31EUA001.ant.amazon.com (10.43.165.15) Precedence: Bulk Subject: [Xen-devel] [PATCH v14 2/5] xenbus/backend: Protect xenbus callback with lock X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: konrad.wilk@oracle.com, pdurrant@amazon.com, SeongJae Park , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, xen-devel@lists.xenproject.org Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" From: SeongJae Park A driver's 'reclaim_memory' callback can race with 'probe' or 'remove' because it will be called whenever memory pressure is detected. To avoid such race, this commit embeds a spinlock in each 'xenbus_device' and make 'xenbus' to hold the lock while the corresponded callbacks are running. Reviewed-by: Juergen Gross Signed-off-by: SeongJae Park --- drivers/xen/xenbus/xenbus_probe.c | 8 +++++++- drivers/xen/xenbus/xenbus_probe_backend.c | 10 ++++++++-- include/xen/xenbus.h | 1 + 3 files changed, 16 insertions(+), 3 deletions(-) diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c index 378486b79f96..66975da4f3b6 100644 --- a/drivers/xen/xenbus/xenbus_probe.c +++ b/drivers/xen/xenbus/xenbus_probe.c @@ -239,7 +239,9 @@ int xenbus_dev_probe(struct device *_dev) goto fail; } + spin_lock(&dev->reclaim_lock); err = drv->probe(dev, id); + spin_unlock(&dev->reclaim_lock); if (err) goto fail_put; @@ -268,8 +270,11 @@ int xenbus_dev_remove(struct device *_dev) free_otherend_watch(dev); - if (drv->remove) + if (drv->remove) { + spin_lock(&dev->reclaim_lock); drv->remove(dev); + spin_unlock(&dev->reclaim_lock); + } module_put(drv->driver.owner); @@ -468,6 +473,7 @@ int xenbus_probe_node(struct xen_bus_type *bus, goto fail; dev_set_name(&xendev->dev, "%s", devname); + spin_lock_init(&xendev->reclaim_lock); /* Register with generic device framework. */ err = device_register(&xendev->dev); diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c index 3b5cb7a5a7e4..791f6fe01e91 100644 --- a/drivers/xen/xenbus/xenbus_probe_backend.c +++ b/drivers/xen/xenbus/xenbus_probe_backend.c @@ -250,12 +250,18 @@ static int backend_probe_and_watch(struct notifier_block *notifier, static int backend_reclaim_memory(struct device *dev, void *data) { const struct xenbus_driver *drv; + struct xenbus_device *xdev; if (!dev->driver) return 0; drv = to_xenbus_driver(dev->driver); - if (drv && drv->reclaim_memory) - drv->reclaim_memory(to_xenbus_device(dev)); + if (drv && drv->reclaim_memory) { + xdev = to_xenbus_device(dev); + if (!spin_trylock(&xdev->reclaim_lock)) + return 0; + drv->reclaim_memory(xdev); + spin_unlock(&xdev->reclaim_lock); + } return 0; } diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h index 980952ea452b..89a889585ba0 100644 --- a/include/xen/xenbus.h +++ b/include/xen/xenbus.h @@ -76,6 +76,7 @@ struct xenbus_device { enum xenbus_state state; struct completion down; struct work_struct work; + spinlock_t reclaim_lock; }; static inline struct xenbus_device *to_xenbus_device(struct device *dev) From patchwork Mon Jan 27 08:18:10 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 11352199 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 01C5914B4 for ; Mon, 27 Jan 2020 08:21:15 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C309420702 for ; Mon, 27 Jan 2020 08:21:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b="sGLs5x1s" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C309420702 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=amazon.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1ivzc2-0001Zz-1A; Mon, 27 Jan 2020 08:19:14 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1ivzc1-0001Zr-E4 for xen-devel@lists.xenproject.org; Mon, 27 Jan 2020 08:19:13 +0000 X-Inumbo-ID: ae33281e-40dd-11ea-9fd7-bc764e2007e4 Received: from smtp-fw-33001.amazon.com (unknown [207.171.190.10]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id ae33281e-40dd-11ea-9fd7-bc764e2007e4; Mon, 27 Jan 2020 08:19:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1580113144; x=1611649144; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=iHRlt6hmfQ9wJIv7m925gNvQQpSwOi/1Yve2xVCNRDc=; b=sGLs5x1sdxLa2Gg1Xq2QTWzyOrKGDVPKHK+k5rLEsv7FL6iXPhJ+vHwY mu6vY0/RJupTBcgrn3h0OoOyr63U9DLnBbmOj6XOdvetol0j4mLskRFss /n/aHAXPYrM04gdSdU7XZ128MXHoEZWZzKC5ccEnYHMlwTL83WWkXkG2x I=; IronPort-SDR: 6R0RfhsiFu7/oLNxqb6mAP/EdsDpGOKvoVBZ9qnakDCRyOha6OjsaOkQiUN5C8Sg8RLn8Bikh2 aIb+eMmevjBw== X-IronPort-AV: E=Sophos;i="5.70,369,1574121600"; d="scan'208";a="22599854" Received: from sea32-co-svc-lb4-vlan3.sea.corp.amazon.com (HELO email-inbound-relay-2b-baacba05.us-west-2.amazon.com) ([10.47.23.38]) by smtp-border-fw-out-33001.sea14.amazon.com with ESMTP; 27 Jan 2020 08:18:51 +0000 Received: from EX13MTAUEA002.ant.amazon.com (pdx4-ws-svc-p6-lb7-vlan2.pdx.amazon.com [10.170.41.162]) by email-inbound-relay-2b-baacba05.us-west-2.amazon.com (Postfix) with ESMTPS id 0FBB2A11F8; Mon, 27 Jan 2020 08:18:51 +0000 (UTC) Received: from EX13D31EUA001.ant.amazon.com (10.43.165.15) by EX13MTAUEA002.ant.amazon.com (10.43.61.77) with Microsoft SMTP Server (TLS) id 15.0.1236.3; Mon, 27 Jan 2020 08:18:50 +0000 Received: from u886c93fd17d25d.ant.amazon.com (10.43.160.8) by EX13D31EUA001.ant.amazon.com (10.43.165.15) with Microsoft SMTP Server (TLS) id 15.0.1367.3; Mon, 27 Jan 2020 08:18:45 +0000 From: To: , , Date: Mon, 27 Jan 2020 09:18:10 +0100 Message-ID: <20200127081812.21216-4-sjpark@amazon.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200127081812.21216-1-sjpark@amazon.com> References: <20200127081812.21216-1-sjpark@amazon.com> MIME-Version: 1.0 X-Originating-IP: [10.43.160.8] X-ClientProxiedBy: EX13D11UWB004.ant.amazon.com (10.43.161.90) To EX13D31EUA001.ant.amazon.com (10.43.165.15) Precedence: Bulk Subject: [Xen-devel] [PATCH v14 3/5] xen/blkback: Squeeze page pools if a memory pressure is detected X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: konrad.wilk@oracle.com, pdurrant@amazon.com, SeongJae Park , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, xen-devel@lists.xenproject.org Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" From: SeongJae Park Each `blkif` has a free pages pool for the grant mapping. The size of the pool starts from zero and is increased on demand while processing the I/O requests. If current I/O requests handling is finished or 100 milliseconds has passed since last I/O requests handling, it checks and shrinks the pool to not exceed the size limit, `max_buffer_pages`. Therefore, host administrators can cause memory pressure in blkback by attaching a large number of block devices and inducing I/O. Such problematic situations can be avoided by limiting the maximum number of devices that can be attached, but finding the optimal limit is not so easy. Improper set of the limit can results in memory pressure or a resource underutilization. This commit avoids such problematic situations by squeezing the pools (returns every free page in the pool to the system) for a while (users can set this duration via a module parameter) if memory pressure is detected. Discussions =========== The `blkback`'s original shrinking mechanism returns only pages in the pool which are not currently be used by `blkback` to the system. In other words, the pages that are not mapped with granted pages. Because this commit is changing only the shrink limit but still uses the same freeing mechanism it does not touch pages which are currently mapping grants. Once memory pressure is detected, this commit keeps the squeezing limit for a user-specified time duration. The duration should be neither too long nor too short. If it is too long, the squeezing incurring overhead can reduce the I/O performance. If it is too short, `blkback` will not free enough pages to reduce the memory pressure. This commit sets the value as `10 milliseconds` by default because it is a short time in terms of I/O while it is a long time in terms of memory operations. Also, as the original shrinking mechanism works for at least every 100 milliseconds, this could be a somewhat reasonable choice. I also tested other durations (refer to the below section for more details) and confirmed that 10 milliseconds is the one that works best with the test. That said, the proper duration depends on actual configurations and workloads. That's why this commit allows users to set the duration as a module parameter. Memory Pressure Test ==================== To show how this commit fixes the memory pressure situation well, I configured a test environment on a xen-running virtualization system. On the `blkfront` running guest instances, I attach a large number of network-backed volume devices and induce I/O to those. Meanwhile, I measure the number of pages that swapped in (pswpin) and out (pswpout) on the `blkback` running guest. The test ran twice, once for the `blkback` before this commit and once for that after this commit. As shown below, this commit has dramatically reduced the memory pressure: pswpin pswpout before 76,672 185,799 after 867 3,967 Optimal Aggressive Shrinking Duration ------------------------------------- To find a best squeezing duration, I repeated the test with three different durations (1ms, 10ms, and 100ms). The results are as below: duration pswpin pswpout 1 707 5,095 10 867 3,967 100 362 3,348 As expected, the memory pressure decreases as the duration increases, but the reduction become slow from the `10ms`. Based on this results, I chose the default duration as 10ms. Performance Overhead Test ========================= This commit could incur I/O performance degradation under severe memory pressure because the squeezing will require more page allocations per I/O. To show the overhead, I artificially made a worst-case squeezing situation and measured the I/O performance of a `blkfront` running guest. For the artificial squeezing, I set the `blkback.max_buffer_pages` using the `/sys/module/xen_blkback/parameters/max_buffer_pages` file. In this test, I set the value to `1024` and `0`. The `1024` is the default value. Setting the value as `0` is same to a situation doing the squeezing always (worst-case). If the underlying block device is slow enough, the squeezing overhead could be hidden. For the reason, I use a fast block device, namely the rbd[1]: # xl block-attach guest phy:/dev/ram0 xvdb w For the I/O performance measurement, I run a simple `dd` command 5 times directly to the device as below and collect the 'MB/s' results. $ for i in {1..5}; do dd if=/dev/zero of=/dev/xvdb \ bs=4k count=$((256*512)); sync; done The results are as below. 'max_pgs' represents the value of the `blkback.max_buffer_pages` parameter. max_pgs Min Max Median Avg Stddev 0 417 423 420 419.4 2.5099801 1024 414 425 416 417.8 4.4384682 No difference proven at 95.0% confidence In short, even worst case squeezing on ramdisk based fast block device makes no visible performance degradation. Please note that this is just a very simple and minimal test. On systems using super-fast block devices and a special I/O workload, the results might be different. If you have any doubt, test on your machine with your workload to find the optimal squeezing duration for you. [1] https://www.kernel.org/doc/html/latest/admin-guide/blockdev/ramdisk.html Reviewed-by: Roger Pau Monné Signed-off-by: SeongJae Park --- .../ABI/testing/sysfs-driver-xen-blkback | 10 +++++++++ drivers/block/xen-blkback/blkback.c | 7 +++++-- drivers/block/xen-blkback/common.h | 1 + drivers/block/xen-blkback/xenbus.c | 21 +++++++++++++++++++ 4 files changed, 37 insertions(+), 2 deletions(-) diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback index 4e7babb3ba1f..ecb7942ff146 100644 --- a/Documentation/ABI/testing/sysfs-driver-xen-blkback +++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback @@ -25,3 +25,13 @@ Description: allocated without being in use. The time is in seconds, 0 means indefinitely long. The default is 60 seconds. + +What: /sys/module/xen_blkback/parameters/buffer_squeeze_duration_ms +Date: December 2019 +KernelVersion: 5.6 +Contact: SeongJae Park +Description: + When memory pressure is reported to blkback this option + controls the duration in milliseconds that blkback will not + cache any page not backed by a grant mapping. + The default is 10ms. diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c index 716b99aa2307..5b9ee0494e15 100644 --- a/drivers/block/xen-blkback/blkback.c +++ b/drivers/block/xen-blkback/blkback.c @@ -656,8 +656,11 @@ int xen_blkif_schedule(void *arg) ring->next_lru = jiffies + msecs_to_jiffies(LRU_INTERVAL); } - /* Shrink if we have more than xen_blkif_max_buffer_pages */ - shrink_free_pagepool(ring, xen_blkif_max_buffer_pages); + /* Shrink the free pages pool if it is too large. */ + if (time_before(jiffies, blkif->buffer_squeeze_end)) + shrink_free_pagepool(ring, 0); + else + shrink_free_pagepool(ring, xen_blkif_max_buffer_pages); if (log_stats && time_after(jiffies, ring->st_print)) print_stats(ring); diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h index 49132b0adbbe..a3eeccf3ac5f 100644 --- a/drivers/block/xen-blkback/common.h +++ b/drivers/block/xen-blkback/common.h @@ -319,6 +319,7 @@ struct xen_blkif { /* All rings for this device. */ struct xen_blkif_ring *rings; unsigned int nr_rings; + unsigned long buffer_squeeze_end; }; struct seg_buf { diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index 4c5d99f87813..55960190b774 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -859,6 +859,26 @@ static void frontend_changed(struct xenbus_device *dev, } +/* Once a memory pressure is detected, squeeze free page pools for a while. */ +static unsigned int buffer_squeeze_duration_ms = 10; +module_param_named(buffer_squeeze_duration_ms, + buffer_squeeze_duration_ms, int, 0644); +MODULE_PARM_DESC(buffer_squeeze_duration_ms, +"Duration in ms to squeeze pages buffer when a memory pressure is detected"); + +/* + * Callback received when the memory pressure is detected. + */ +static void reclaim_memory(struct xenbus_device *dev) +{ + struct backend_info *be = dev_get_drvdata(&dev->dev); + + if (!be) + return; + be->blkif->buffer_squeeze_end = jiffies + + msecs_to_jiffies(buffer_squeeze_duration_ms); +} + /* ** Connection ** */ @@ -1152,6 +1172,7 @@ static struct xenbus_driver xen_blkbk_driver = { .remove = xen_blkbk_remove, .otherend_changed = frontend_changed, .allow_rebind = true, + .reclaim_memory = reclaim_memory, }; int xen_blkif_xenbus_init(void) From patchwork Mon Jan 27 08:18:11 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 11352195 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 11A25159A for ; Mon, 27 Jan 2020 08:21:01 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E1A972168B for ; Mon, 27 Jan 2020 08:21:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b="cVFY4MWx" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E1A972168B Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=amazon.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1ivzbl-0001Vn-TG; Mon, 27 Jan 2020 08:18:57 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1ivzbl-0001Vg-6C for xen-devel@lists.xenproject.org; Mon, 27 Jan 2020 08:18:57 +0000 X-Inumbo-ID: a9a70c66-40dd-11ea-84ee-12813bfff9fa Received: from smtp-fw-6001.amazon.com (unknown [52.95.48.154]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id a9a70c66-40dd-11ea-84ee-12813bfff9fa; Mon, 27 Jan 2020 08:18:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1580113137; x=1611649137; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=qgsEpK440x1XE1YWBsqFTbCHtBMaQUS99dZvFwIFhyk=; b=cVFY4MWxbv08jg/tyfi1ty+4zBTWh6DzUjU20oGL0GK3SrzMDzfQlUUQ XhXgx/KzHZgT2Fe5Mkk4K4d96yEK63ufPm+2xZuE+N81hJJG4rVNND4dY c9Hu0qNQS5X2lrnGu5n42Vqak7v+H3Y/NXWIcGDnjX80aweA5qJU9mdJ7 c=; IronPort-SDR: 7zhVlLasSLx/+Ff4QeoD5a0IbtFH4DaFsyUL9Zh4X9N5G1oQdI9YmtaB2mUOlOw/d5KkGYtW5a gI4LziEm4kQw== X-IronPort-AV: E=Sophos;i="5.70,369,1574121600"; d="scan'208";a="14867875" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-2c-4e7c8266.us-west-2.amazon.com) ([10.43.8.6]) by smtp-border-fw-out-6001.iad6.amazon.com with ESMTP; 27 Jan 2020 08:18:56 +0000 Received: from EX13MTAUEA002.ant.amazon.com (pdx4-ws-svc-p6-lb7-vlan2.pdx.amazon.com [10.170.41.162]) by email-inbound-relay-2c-4e7c8266.us-west-2.amazon.com (Postfix) with ESMTPS id 1BF3AA06AB; Mon, 27 Jan 2020 08:18:55 +0000 (UTC) Received: from EX13D31EUA001.ant.amazon.com (10.43.165.15) by EX13MTAUEA002.ant.amazon.com (10.43.61.77) with Microsoft SMTP Server (TLS) id 15.0.1236.3; Mon, 27 Jan 2020 08:18:54 +0000 Received: from u886c93fd17d25d.ant.amazon.com (10.43.160.8) by EX13D31EUA001.ant.amazon.com (10.43.165.15) with Microsoft SMTP Server (TLS) id 15.0.1367.3; Mon, 27 Jan 2020 08:18:50 +0000 From: To: , , Date: Mon, 27 Jan 2020 09:18:11 +0100 Message-ID: <20200127081812.21216-5-sjpark@amazon.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200127081812.21216-1-sjpark@amazon.com> References: <20200127081812.21216-1-sjpark@amazon.com> MIME-Version: 1.0 X-Originating-IP: [10.43.160.8] X-ClientProxiedBy: EX13D11UWB004.ant.amazon.com (10.43.161.90) To EX13D31EUA001.ant.amazon.com (10.43.165.15) Precedence: Bulk Subject: [Xen-devel] [PATCH v14 4/5] xen/blkback: Remove unnecessary static variable name prefixes X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: konrad.wilk@oracle.com, pdurrant@amazon.com, SeongJae Park , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, xen-devel@lists.xenproject.org Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" From: SeongJae Park A few of static variables in blkback have 'xen_blkif_' prefix, though it is unnecessary for static variables. This commit removes such prefixes. Reviewed-by: Roger Pau Monné Signed-off-by: SeongJae Park --- drivers/block/xen-blkback/blkback.c | 37 +++++++++++++---------------- 1 file changed, 17 insertions(+), 20 deletions(-) diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c index 5b9ee0494e15..c2f71265af4b 100644 --- a/drivers/block/xen-blkback/blkback.c +++ b/drivers/block/xen-blkback/blkback.c @@ -62,8 +62,8 @@ * IO workloads. */ -static int xen_blkif_max_buffer_pages = 1024; -module_param_named(max_buffer_pages, xen_blkif_max_buffer_pages, int, 0644); +static int max_buffer_pages = 1024; +module_param_named(max_buffer_pages, max_buffer_pages, int, 0644); MODULE_PARM_DESC(max_buffer_pages, "Maximum number of free pages to keep in each block backend buffer"); @@ -78,8 +78,8 @@ MODULE_PARM_DESC(max_buffer_pages, * algorithm. */ -static int xen_blkif_max_pgrants = 1056; -module_param_named(max_persistent_grants, xen_blkif_max_pgrants, int, 0644); +static int max_pgrants = 1056; +module_param_named(max_persistent_grants, max_pgrants, int, 0644); MODULE_PARM_DESC(max_persistent_grants, "Maximum number of grants to map persistently"); @@ -88,8 +88,8 @@ MODULE_PARM_DESC(max_persistent_grants, * use. The time is in seconds, 0 means indefinitely long. */ -static unsigned int xen_blkif_pgrant_timeout = 60; -module_param_named(persistent_grant_unused_seconds, xen_blkif_pgrant_timeout, +static unsigned int pgrant_timeout = 60; +module_param_named(persistent_grant_unused_seconds, pgrant_timeout, uint, 0644); MODULE_PARM_DESC(persistent_grant_unused_seconds, "Time in seconds an unused persistent grant is allowed to " @@ -137,9 +137,8 @@ module_param(log_stats, int, 0644); static inline bool persistent_gnt_timeout(struct persistent_gnt *persistent_gnt) { - return xen_blkif_pgrant_timeout && - (jiffies - persistent_gnt->last_used >= - HZ * xen_blkif_pgrant_timeout); + return pgrant_timeout && (jiffies - persistent_gnt->last_used >= + HZ * pgrant_timeout); } static inline int get_free_page(struct xen_blkif_ring *ring, struct page **page) @@ -234,7 +233,7 @@ static int add_persistent_gnt(struct xen_blkif_ring *ring, struct persistent_gnt *this; struct xen_blkif *blkif = ring->blkif; - if (ring->persistent_gnt_c >= xen_blkif_max_pgrants) { + if (ring->persistent_gnt_c >= max_pgrants) { if (!blkif->vbd.overflow_max_grants) blkif->vbd.overflow_max_grants = 1; return -EBUSY; @@ -397,14 +396,13 @@ static void purge_persistent_gnt(struct xen_blkif_ring *ring) goto out; } - if (ring->persistent_gnt_c < xen_blkif_max_pgrants || - (ring->persistent_gnt_c == xen_blkif_max_pgrants && + if (ring->persistent_gnt_c < max_pgrants || + (ring->persistent_gnt_c == max_pgrants && !ring->blkif->vbd.overflow_max_grants)) { num_clean = 0; } else { - num_clean = (xen_blkif_max_pgrants / 100) * LRU_PERCENT_CLEAN; - num_clean = ring->persistent_gnt_c - xen_blkif_max_pgrants + - num_clean; + num_clean = (max_pgrants / 100) * LRU_PERCENT_CLEAN; + num_clean = ring->persistent_gnt_c - max_pgrants + num_clean; num_clean = min(ring->persistent_gnt_c, num_clean); pr_debug("Going to purge at least %u persistent grants\n", num_clean); @@ -599,8 +597,7 @@ static void print_stats(struct xen_blkif_ring *ring) current->comm, ring->st_oo_req, ring->st_rd_req, ring->st_wr_req, ring->st_f_req, ring->st_ds_req, - ring->persistent_gnt_c, - xen_blkif_max_pgrants); + ring->persistent_gnt_c, max_pgrants); ring->st_print = jiffies + msecs_to_jiffies(10 * 1000); ring->st_rd_req = 0; ring->st_wr_req = 0; @@ -660,7 +657,7 @@ int xen_blkif_schedule(void *arg) if (time_before(jiffies, blkif->buffer_squeeze_end)) shrink_free_pagepool(ring, 0); else - shrink_free_pagepool(ring, xen_blkif_max_buffer_pages); + shrink_free_pagepool(ring, max_buffer_pages); if (log_stats && time_after(jiffies, ring->st_print)) print_stats(ring); @@ -887,7 +884,7 @@ static int xen_blkbk_map(struct xen_blkif_ring *ring, continue; } if (use_persistent_gnts && - ring->persistent_gnt_c < xen_blkif_max_pgrants) { + ring->persistent_gnt_c < max_pgrants) { /* * We are using persistent grants, the grant is * not mapped but we might have room for it. @@ -914,7 +911,7 @@ static int xen_blkbk_map(struct xen_blkif_ring *ring, pages[seg_idx]->persistent_gnt = persistent_gnt; pr_debug("grant %u added to the tree of persistent grants, using %u/%u\n", persistent_gnt->gnt, ring->persistent_gnt_c, - xen_blkif_max_pgrants); + max_pgrants); goto next; } if (use_persistent_gnts && !blkif->vbd.overflow_max_grants) { From patchwork Mon Jan 27 08:19:57 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 11352201 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E38FC14B4 for ; Mon, 27 Jan 2020 08:22:21 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id BE6B721569 for ; Mon, 27 Jan 2020 08:22:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b="HSWJjL3q" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BE6B721569 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=amazon.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1ivzdF-0002PE-Eq; Mon, 27 Jan 2020 08:20:29 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1ivzdE-0002P4-7M for xen-devel@lists.xenproject.org; Mon, 27 Jan 2020 08:20:28 +0000 X-Inumbo-ID: db33ec68-40dd-11ea-9fd7-bc764e2007e4 Received: from smtp-fw-6001.amazon.com (unknown [52.95.48.154]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id db33ec68-40dd-11ea-9fd7-bc764e2007e4; Mon, 27 Jan 2020 08:20:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1580113220; x=1611649220; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=I0bGMY0UnkD1SQDKudWK+VHlWYQo9kxn8xvkLvZ6+gw=; b=HSWJjL3qZflBjg3HZ0LsIxgvkt4awx+NFDm2/U2UIxmjPWlrrcpE9WW4 NTX43GtRXtGQUrmrJvoeLi8KjxFsvNJo7AcfjhdTFS4wYHwiYnUBprd+r A7Un1iA0KAAyidTl2bIksrAXoIoMjYsr9pvTKjN38Ze/OVxMjm1vxQgWD I=; IronPort-SDR: nJ6CGo/h7Rj8evct5993fDuaqqM8Fs4H2y02wDFZ2uT5VCpoe44uYjQlucDgefYn99dFDE3SE8 G+O8acrjKseA== X-IronPort-AV: E=Sophos;i="5.70,369,1574121600"; d="scan'208";a="14868091" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-2b-a7fdc47a.us-west-2.amazon.com) ([10.43.8.6]) by smtp-border-fw-out-6001.iad6.amazon.com with ESMTP; 27 Jan 2020 08:20:20 +0000 Received: from EX13MTAUEA002.ant.amazon.com (pdx4-ws-svc-p6-lb7-vlan2.pdx.amazon.com [10.170.41.162]) by email-inbound-relay-2b-a7fdc47a.us-west-2.amazon.com (Postfix) with ESMTPS id 2F458C5A7D; Mon, 27 Jan 2020 08:20:16 +0000 (UTC) Received: from EX13D31EUA001.ant.amazon.com (10.43.165.15) by EX13MTAUEA002.ant.amazon.com (10.43.61.77) with Microsoft SMTP Server (TLS) id 15.0.1236.3; Mon, 27 Jan 2020 08:20:16 +0000 Received: from u886c93fd17d25d.ant.amazon.com (10.43.161.78) by EX13D31EUA001.ant.amazon.com (10.43.165.15) with Microsoft SMTP Server (TLS) id 15.0.1367.3; Mon, 27 Jan 2020 08:20:11 +0000 From: To: , , Date: Mon, 27 Jan 2020 09:19:57 +0100 Message-ID: <20200127081957.21509-1-sjpark@amazon.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200127081812.21216-1-sjpark@amazon.com> References: <20200127081812.21216-1-sjpark@amazon.com> MIME-Version: 1.0 X-Originating-IP: [10.43.161.78] X-ClientProxiedBy: EX13D25UWB001.ant.amazon.com (10.43.161.245) To EX13D31EUA001.ant.amazon.com (10.43.165.15) Precedence: Bulk Subject: [Xen-devel] [PATCH v14 5/5] xen/blkback: Consistently insert one empty line between functions X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: konrad.wilk@oracle.com, pdurrant@amazon.com, SeongJae Park , linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, xen-devel@lists.xenproject.org Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" From: SeongJae Park The number of empty lines between functions in the xenbus.c is inconsistent. This trivial style cleanup commit fixes the file to consistently place only one empty line. Acked-by: Roger Pau Monné Signed-off-by: SeongJae Park --- drivers/block/xen-blkback/xenbus.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index 55960190b774..42944d41aea0 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -467,7 +467,6 @@ static void xenvbd_sysfs_delif(struct xenbus_device *dev) device_remove_file(&dev->dev, &dev_attr_physical_device); } - static void xen_vbd_free(struct xen_vbd *vbd) { if (vbd->bdev) @@ -524,6 +523,7 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle, handle, blkif->domid); return 0; } + static int xen_blkbk_remove(struct xenbus_device *dev) { struct backend_info *be = dev_get_drvdata(&dev->dev); @@ -607,6 +607,7 @@ static void xen_blkbk_discard(struct xenbus_transaction xbt, struct backend_info if (err) dev_warn(&dev->dev, "writing feature-discard (%d)", err); } + int xen_blkbk_barrier(struct xenbus_transaction xbt, struct backend_info *be, int state) { @@ -691,7 +692,6 @@ static int xen_blkbk_probe(struct xenbus_device *dev, return err; } - /* * Callback received when the hotplug scripts have placed the physical-device * node. Read it and the mode node, and create a vbd. If the frontend is @@ -783,7 +783,6 @@ static void backend_changed(struct xenbus_watch *watch, } } - /* * Callback received when the frontend's state changes. */ @@ -858,7 +857,6 @@ static void frontend_changed(struct xenbus_device *dev, } } - /* Once a memory pressure is detected, squeeze free page pools for a while. */ static unsigned int buffer_squeeze_duration_ms = 10; module_param_named(buffer_squeeze_duration_ms, @@ -881,7 +879,6 @@ static void reclaim_memory(struct xenbus_device *dev) /* ** Connection ** */ - /* * Write the physical details regarding the block device to the store, and * switch to Connected state.