From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by kanga.kvack.org (Postfix) with ESMTP id 542C36B0010 for ; Wed, 8 Aug 2018 03:38:38 -0400 (EDT) Received: by mail-wr1-f72.google.com with SMTP id w2-v6so1088471wrt.13 for ; Wed, 08 Aug 2018 00:38:38 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id i18-v6sor1395299wrm.33.2018.08.08.00.38.37 for (Google Transport Security); Wed, 08 Aug 2018 00:38:37 -0700 (PDT) Date: Wed, 8 Aug 2018 09:38:35 +0200 From: Oscar Salvador Subject: Re: [RFC PATCH 2/3] mm/memory_hotplug: Create __shrink_pages and move it to offline_pages Message-ID: <20180808073835.GA9568@techadventures.net> References: <20180807133757.18352-1-osalvador@techadventures.net> <20180807133757.18352-3-osalvador@techadventures.net> <20180807135221.GA3301@redhat.com> <20180807204834.GA6844@techadventures.net> <20180807221345.GD3301@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180807221345.GD3301@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Jerome Glisse Cc: David Hildenbrand , akpm@linux-foundation.org, mhocko@suse.com, dan.j.williams@intel.com, pasha.tatashin@oracle.com, yasu.isimatu@gmail.com, logang@deltatee.com, dave.jiang@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Oscar Salvador On Tue, Aug 07, 2018 at 06:13:45PM -0400, Jerome Glisse wrote: > > And since we know for sure that memhotplug-code cannot call it with ZONE_DEVICE, > > I think this can be done easily. > > This might change down road but for now this is correct. They are > talks to enumerate device memory through standard platform mechanisms > and thus the kernel might see new types of resources down the road and > maybe we will want to hotplug them directly from regular hotplug path > as ZONE_DEVICE (lot of hypothetical at this point ;)). Well, I think that if that happens this whole thing will become much easier, since we will not have several paths for doing the same thing. Another thing that I realized is that while we want to move all operation-pages from remove_memory() path to offline_pages(), this can get tricky. Unless I am missing something, the devices from HMM and devm are not being registered against "memory_subsys" struct, and so, they never get to call memory_subsys_offline() and so offline_pages(). Which means that we would have to call __remove_zone() from those paths. But this alone will not work. find_smallest/biggest_section_pfn are two functions that are being called from shrink_pgdat_span and shrink_zone_span to adjust zone_first_pfn/node_first_pfn and the spanned pages. Currently, find_smallest/biggest_section_pfn checks for the secion to be valid, and this is fine since we are removing those sections from the remove_memory path. But if we want to move __remove_zone() to offline_pages(), we have to use online_section() instead of valid_section(). This is all fine from offline_pages because the sections get offlined in: __offline_pages offline_isolated_pages offline_isolated_pages_cb __offline_isolated_pages offline_mem_sections But this does not happen in HMM/devm path. I am pretty sure this is a dumb question, but why HMM/devm path do not call online_pages/offline_pages? Thanks -- Oscar Salvador SUSE L3