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 17A5EC433DB for ; Tue, 2 Feb 2021 08:51:15 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9299064E2B for ; Tue, 2 Feb 2021 08:51:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9299064E2B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 1DC776B006C; Tue, 2 Feb 2021 03:51:14 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 166B26B006E; Tue, 2 Feb 2021 03:51:14 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0546E6B0070; Tue, 2 Feb 2021 03:51:13 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0041.hostedemail.com [216.40.44.41]) by kanga.kvack.org (Postfix) with ESMTP id DCE3A6B006C for ; Tue, 2 Feb 2021 03:51:13 -0500 (EST) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id AA2DB8249980 for ; Tue, 2 Feb 2021 08:51:13 +0000 (UTC) X-FDA: 77772708426.02.need51_5f15aae275c9 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin02.hostedemail.com (Postfix) with ESMTP id 8CD0810097AA2 for ; Tue, 2 Feb 2021 08:51:13 +0000 (UTC) X-HE-Tag: need51_5f15aae275c9 X-Filterd-Recvd-Size: 3501 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf17.hostedemail.com (Postfix) with ESMTP for ; Tue, 2 Feb 2021 08:51:12 +0000 (UTC) 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) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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