From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751213AbdFBOVS (ORCPT ); Fri, 2 Jun 2017 10:21:18 -0400 Received: from mail-sn1nam02on0065.outbound.protection.outlook.com ([104.47.36.65]:59211 "EHLO NAM02-SN1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750971AbdFBOVQ (ORCPT ); Fri, 2 Jun 2017 10:21:16 -0400 Authentication-Results: vger.kernel.org; dkim=none (message not signed) header.d=none;vger.kernel.org; dmarc=none action=none header.from=amd.com; Subject: Re: strange PAGE_ALLOC_COSTLY_ORDER usage in xgbe_map_rx_buffer To: Michal Hocko Cc: linux-mm@kvack.org, LKML References: <20170531160422.GW27783@dhcp22.suse.cz> From: Tom Lendacky Message-ID: <4b894f15-6876-8598-def5-8113df836750@amd.com> Date: Fri, 2 Jun 2017 09:20:54 -0500 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: <20170531160422.GW27783@dhcp22.suse.cz> Content-Type: text/plain; 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> which looks quite suspicious. Why does it PAGE_ALLOC_COSTLY_ORDER - 1? > And why do you depend on PAGE_ALLOC_COSTLY_ORDER at all? > The driver tries to allocate a number of pages to be used as receive buffers. Based on what I could find in documentation, the value of PAGE_ALLOC_COSTLY_ORDER is the point at which order allocations (could) get expensive. So I decrease by one the order requested. The max_t test is just to insure that in case PAGE_ALLOC_COSTLY_ORDER ever gets defined as 0, 0 would be used. I believe there have been some enhancements relative to speed in allocating 0-order pages recently that may make this unnecessary. I haven't run any performance tests yet to determine if I can just go to a 0-order allocation, though. Thanks, Tom > Thanks! >