From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4DBB4C67863 for ; Fri, 19 Oct 2018 02:18:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0930721477 for ; Fri, 19 Oct 2018 02:18:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0930721477 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727010AbeJSKWY (ORCPT ); Fri, 19 Oct 2018 06:22:24 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:39210 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726463AbeJSKWY (ORCPT ); Fri, 19 Oct 2018 06:22:24 -0400 Received: from localhost.localdomain (c-24-4-154-175.hsd1.ca.comcast.net [24.4.154.175]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 22097C49; Fri, 19 Oct 2018 02:18:27 +0000 (UTC) Date: Thu, 18 Oct 2018 19:18:25 -0700 From: Andrew Morton To: Michal Hocko Cc: Arun KS , Vlastimil Babka , kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com, boris.ostrovsky@oracle.com, jgross@suse.com, dan.j.williams@intel.com, iamjoonsoo.kim@lge.com, gregkh@linuxfoundation.org, osalvador@suse.de, malat@debian.org, kirill.shutemov@linux.intel.com, jrdr.linux@gmail.com, yasu.isimatu@gmail.com, mgorman@techsingularity.net, aaron.lu@intel.com, devel@linuxdriverproject.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, xen-devel@lists.xenproject.org, vatsa@codeaurora.org, vinmenon@codeaurora.org, getarunks@gmail.com Subject: Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order Message-Id: <20181018191825.fcad6e28f32a3686f201acdf@linux-foundation.org> In-Reply-To: <20181011075503.GQ5873@dhcp22.suse.cz> References: <1538727006-5727-1-git-send-email-arunks@codeaurora.org> <72215e75-6c7e-0aef-c06e-e3aba47cf806@suse.cz> <20181010173334.GL5873@dhcp22.suse.cz> <20181011075503.GQ5873@dhcp22.suse.cz> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 11 Oct 2018 09:55:03 +0200 Michal Hocko wrote: > > > > > This is now not called anymore, although the xen/hv variants still do > > > > > it. The function seems empty these days, maybe remove it as a followup > > > > > cleanup? > > > > > > > > > > > - __online_page_increment_counters(page); > > > > > > - __online_page_free(page); > > > > > > + __free_pages_core(page, order); > > > > > > + totalram_pages += (1UL << order); > > > > > > +#ifdef CONFIG_HIGHMEM > > > > > > + if (PageHighMem(page)) > > > > > > + totalhigh_pages += (1UL << order); > > > > > > +#endif > > > > > > > > > > __online_page_increment_counters() would have used > > > > > adjust_managed_page_count() which would do the changes under > > > > > managed_page_count_lock. Are we safe without the lock? If yes, there > > > > > should perhaps be a comment explaining why. > > > > > > > > Looks unsafe without managed_page_count_lock. > > > > > > Why does it matter actually? We cannot online/offline memory in > > > parallel. This is not the case for the boot where we initialize memory > > > in parallel on multiple nodes. So this seems to be safe currently unless > > > I am missing something. A comment explaining that would be helpful > > > though. > > > > Other main callers of adjust_manage_page_count(), > > > > static inline void free_reserved_page(struct page *page) > > { > > __free_reserved_page(page); > > adjust_managed_page_count(page, 1); > > } > > > > static inline void mark_page_reserved(struct page *page) > > { > > SetPageReserved(page); > > adjust_managed_page_count(page, -1); > > } > > > > Won't they race with memory hotplug? > > > > Few more, > > ./drivers/xen/balloon.c:519: adjust_managed_page_count(page, -1); > > ./drivers/virtio/virtio_balloon.c:175: adjust_managed_page_count(page, -1); > > ./drivers/virtio/virtio_balloon.c:196: adjust_managed_page_count(page, 1); > > ./mm/hugetlb.c:2158: adjust_managed_page_count(page, 1 << > > h->order); > > They can, and I have missed those. So this patch needs more work, yes?