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=-8.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,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 E76D0C433DB for ; Wed, 3 Feb 2021 14:13:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9B0E464F41 for ; Wed, 3 Feb 2021 14:13:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232583AbhBCONw (ORCPT ); Wed, 3 Feb 2021 09:13:52 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:34568 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231936AbhBCONp (ORCPT ); Wed, 3 Feb 2021 09:13:45 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612361539; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=B4H8QwsmVhRse/MHW6XyL15Amm7fwPxllon0PusjMy0=; b=TerdKgvvZQ/dFepReMZedcC3AYNJk8RLZT2Dhuu2+pDLzJF0K32Hvr+/qgYQSru0f8CvF7 wVXv7XVZrcKZFbYgKmHo2SKH1LezUVi8P8tHn1qzqEAGYPbChsftflWDbwxwAWvOKzGZG7 QvMMzMOGdElGaiPK4lQmECGpHaDUNG4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-559-fB7sa8X1OhGlTzBcYzEIGg-1; Wed, 03 Feb 2021 09:12:12 -0500 X-MC-Unique: fB7sa8X1OhGlTzBcYzEIGg-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2F04B100C660; Wed, 3 Feb 2021 14:12:09 +0000 (UTC) Received: from [10.36.112.222] (ovpn-112-222.ams2.redhat.com [10.36.112.222]) by smtp.corp.redhat.com (Postfix) with ESMTP id C887760C71; Wed, 3 Feb 2021 14:12:06 +0000 (UTC) Subject: Re: [PATCH v2 2/3] x86/vmemmap: Drop handling of 1GB vmemmap ranges To: Oscar Salvador 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 References: <20210203104750.23405-1-osalvador@suse.de> <20210203104750.23405-3-osalvador@suse.de> <20210203141038.GA26693@linux> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Wed, 3 Feb 2021 15:12:05 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20210203141038.GA26693@linux> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03.02.21 15:10, Oscar Salvador wrote: > On Wed, Feb 03, 2021 at 02:33:56PM +0100, David Hildenbrand wrote: >> One problem I see with existing code / this change making more obvious is >> that when trying to remove in other granularity than we added (e.g., unplug >> a 128MB DIMM avaialble during boot), we remove the direct map of unrelated >> DIMMs. > > So, let me see if I understand your concern. > > We have a range that was mapped with 1GB page, and we try to remove > a 128MB chunk from it. > Yes, in that case we would clear the pud, and that is bad, so we should > keep the PAGE_ALIGNED checks. > > Now, let us assume that scenario. > If you have a 1GB mapped range and you remove it in smaller chunks bit by bit > (e.g: 128M), the direct mapping of that range will never be cleared unless No, that's exactly what's happening. Good thing is that it barely ever happens, so I assume leaving behind some direct mapping / page tables is not that bad. -- Thanks, David / dhildenb