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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 38C44C433E9 for ; Tue, 2 Feb 2021 08:52:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EED7A64F62 for ; Tue, 2 Feb 2021 08:52:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232814AbhBBIwB (ORCPT ); Tue, 2 Feb 2021 03:52:01 -0500 Received: from mx2.suse.de ([195.135.220.15]:44910 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232354AbhBBIvy (ORCPT ); Tue, 2 Feb 2021 03:51:54 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 85868AEB3; Tue, 2 Feb 2021 08:51:11 +0000 (UTC) Date: Tue, 2 Feb 2021 09:51:09 +0100 From: Oscar Salvador To: David Hildenbrand Cc: Andrew Morton , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H . Peter Anvin" , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] x86/vmemmap: Handle unpopulated sub-pmd ranges Message-ID: <20210202085100.GA8263@linux> References: <20210129064045.18471-1-osalvador@suse.de> <20210202075243.GA7037@linux> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 02, 2021 at 09:35:09AM +0100, David Hildenbrand wrote: > Yeah, last time I raised it was in > > https://lkml.kernel.org/r/20200703013435.GA11340@L-31X9LVDL-1304.local > > but I never got to clean it up myself. I see. > > So, IIRC we have two cases during hotplug: > > 1) the ones that want memory blocks > > 2) the ones that do not want them (pmem stuff) > > > > For #1, we always enforce section alignment in add_memory_resource, and for > > #2 we always make sure the range is at least sub-section aligned. > > > > And the important stuff is that boot memory is no longer to be hot-removed > > (boot memory had some strange layout sometimes). > > The vmemmap of boot mem sections is always fully populated, even with > strange memory layouts (e.g., see comment in pfn_valid()). In addition, we > can only offline+remove whole sections, so that should be fine. You are right. > > > > > So, given the above, I think it should be safe to drop that check in > > remote_pte_table. > > But do we really need to force page alignment in vmemmap_populate/vmemmap_free? > > vmemmap_populate should already receive a page-aligned chunk because > > __populate_section_memmap made sure of that, and vmemmap_free() should be ok > > as we already filtered out at hot-adding stage. > > > > Of course, this will hold as long as struct page size of multiple of 8. > > Should that change we might get trouble, but I do not think that can ever > > happened (tm). > > > > But anyway, I am fine with placing a couple of checks in vmemmap_{populate,free} > > just to double check. > > > > What do you think? > > I'd just throw in 1 or 2 VM_BUG_ON() to self-document what we expect and > that we thought about these conditions. It's then easy to identify the > relevant commit where we explain the rationale. Fine by me, also on a second thought it is good to have some sort of clue when looking at the code. I will add that cleanup before the actual "fix" of the sub-pmd stuff. thanks! -- Oscar Salvador SUSE L3