From nobody Sun Apr 19 13:43:33 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 23BD4C43334 for ; Thu, 30 Jun 2022 07:33:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232853AbiF3Hd3 (ORCPT ); Thu, 30 Jun 2022 03:33:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55866 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232851AbiF3Hd1 (ORCPT ); Thu, 30 Jun 2022 03:33:27 -0400 Received: from mga06.intel.com (mga06b.intel.com [134.134.136.31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DA2133334B for ; Thu, 30 Jun 2022 00:33:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1656574406; x=1688110406; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=yS4Suwf7GI6LhylNscWfzZ0ukkPLH++SXvgQgtpNGaQ=; b=OlzD+6hY0HhiFHVXz3+edKtKH/6Ai6+DJiKdUKmeJ1QiwyH55DGWZwKg 7/UCM8akS0OMiHVmL9eUBNefmxOE6J4cFdzNZOCLv1mwbyCSz2J8VtoQd Ci8G4dLZYdLF5O0M9lXiF2Z46bA4xVDby8nLfgzO+kZ1k6zA3huUBVSdm kKIwZ/EaQSi6cD10RVvxBQ07mQODaZGNiVrJCNhETIgthS0R3zhHtdbmf SIGTiNUr3KNXhyxusjSZ/l7l4pJry2NbVZn+X9wQsQoEZ/WTrdaRTIruM WTX4NIjxfdw/0cY/+8tAcJdc/LneM7PbcEtx+EhhlZMqzUgD3d9Q/8hQY g==; X-IronPort-AV: E=McAfee;i="6400,9594,10393"; a="343960417" X-IronPort-AV: E=Sophos;i="5.92,233,1650956400"; d="scan'208";a="343960417" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Jun 2022 00:33:08 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.92,233,1650956400"; d="scan'208";a="680866208" Received: from shbuild999.sh.intel.com ([10.239.146.138]) by FMSMGA003.fm.intel.com with ESMTP; 30 Jun 2022 00:33:05 -0700 From: Feng Tang To: Joerg Roedel , Will Deacon , Robin Murphy , iommu@lists.linux-foundation.org, iommu@lists.linux.dev, Andrew Morton , Christoph Lameter , Vlastimil Babka Cc: linux-mm@kvack.org, Paul Menzel , linux-kernel@vger.kernel.org, Feng Tang Subject: [PATCH] iommu/iova: change IOVA_MAG_SIZE to 127 to save memory Date: Thu, 30 Jun 2022 15:33:04 +0800 Message-Id: <20220630073304.26945-1-feng.tang@intel.com> X-Mailer: git-send-email 2.27.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" kmalloc will round up the request size to power of 2, and current iova_magazine's size is 1032 (1024+8) bytes, so each instance allocated will get 2048 bytes from kmalloc, causing around 1KB waste. And in some exstreme case, the memory wasted can trigger OOM as reported in 2019 on a crash kernel with 256 MB memory [1]. [ 4.319253] iommu: Adding device 0000:06:00.2 to group 5 [ 4.325869] iommu: Adding device 0000:20:01.0 to group 15 [ 4.332648] iommu: Adding device 0000:20:02.0 to group 16 [ 4.338946] swapper/0 invoked oom-killer: gfp_mask=3D0x6040c0(GFP_KERN= EL|__GFP_COMP), nodemask=3D(null), order=3D0, oom_score_adj=3D0 [ 4.350251] swapper/0 cpuset=3D/ mems_allowed=3D0 [ 4.354618] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.19.57.mx64.282= #1 [ 4.355612] Hardware name: Dell Inc. PowerEdge R7425/08V001, BIOS 1.9.= 3 06/25/2019 [ 4.355612] Call Trace: [ 4.355612] dump_stack+0x46/0x5b [ 4.355612] dump_header+0x6b/0x289 [ 4.355612] out_of_memory+0x470/0x4c0 [ 4.355612] __alloc_pages_nodemask+0x970/0x1030 [ 4.355612] cache_grow_begin+0x7d/0x520 [ 4.355612] fallback_alloc+0x148/0x200 [ 4.355612] kmem_cache_alloc_trace+0xac/0x1f0 [ 4.355612] init_iova_domain+0x112/0x170 [ 4.355612] amd_iommu_domain_alloc+0x138/0x1a0 [ 4.355612] iommu_group_get_for_dev+0xc4/0x1a0 [ 4.355612] amd_iommu_add_device+0x13a/0x610 [ 4.355612] add_iommu_group+0x20/0x30 [ 4.355612] bus_for_each_dev+0x76/0xc0 [ 4.355612] bus_set_iommu+0xb6/0xf0 [ 4.355612] amd_iommu_init_api+0x112/0x132 [ 4.355612] state_next+0xfb1/0x1165 [ 4.355612] amd_iommu_init+0x1f/0x67 [ 4.355612] pci_iommu_init+0x16/0x3f ... [ 4.670295] Unreclaimable slab info: ... [ 4.857565] kmalloc-2048 59164KB 59164KB Change IOVA_MAG_SIZE from 128 to 127 to make size of 'iova_magazine' 1024 bytes so that no memory will be wasted. [1]. https://lkml.org/lkml/2019/8/12/266 Signed-off-by: Feng Tang Acked-by: Robin Murphy --- drivers/iommu/iova.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c index db77aa675145b..27634ddd9b904 100644 --- a/drivers/iommu/iova.c +++ b/drivers/iommu/iova.c @@ -614,7 +614,12 @@ EXPORT_SYMBOL_GPL(reserve_iova); * dynamic size tuning described in the paper. */ =20 -#define IOVA_MAG_SIZE 128 +/* + * As kmalloc's buffer size is fixed to power of 2, 127 is chosen to + * assure size of 'iova_magzine' to be 1024 bytes, so that no memory + * will be wasted. + */ +#define IOVA_MAG_SIZE 127 #define MAX_GLOBAL_MAGS 32 /* magazines per bin */ =20 struct iova_magazine { --=20 2.27.0