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=-9.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=unavailable 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 AE6C8C433E1 for ; Sun, 16 Aug 2020 12:54:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8A0F720826 for ; Sun, 16 Aug 2020 12:54:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="iltL6dXY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729033AbgHPMy3 (ORCPT ); Sun, 16 Aug 2020 08:54:29 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:48937 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728737AbgHPMyU (ORCPT ); Sun, 16 Aug 2020 08:54:20 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1597582458; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=8nxqR9uPQACL0xkU7YbF8gHsqM4mKp3ngfuFmHvhdpc=; b=iltL6dXYvDzfuq0TGdr6P2uiIemS3RHnXJC8Uqgu1FdvoH4jFQ0jNFBWuHcX+p/YUfoX+d pVBnFsvkRnomBV9ju2dT+EnTduFkM4FKoq5QiBqpbtoVYL4kJJJPckEGZuC80XdGbGFjbw O9drQkROq+JvgJ1/n6V52qa/+Bj2+1A= 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-397-YGA3H13dNmCfnHW-TTGgFw-1; Sun, 16 Aug 2020 08:54:14 -0400 X-MC-Unique: YGA3H13dNmCfnHW-TTGgFw-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 7A26E802B47; Sun, 16 Aug 2020 12:54:12 +0000 (UTC) Received: from t480s.redhat.com (ovpn-112-43.ams2.redhat.com [10.36.112.43]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1EEE16E72F; Sun, 16 Aug 2020 12:54:06 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: virtualization@lists.linux-foundation.org, linux-mm@kvack.org, David Hildenbrand , Mike Rapoport , Andrew Morton , Michal Hocko , "Michael S . Tsirkin" , Mike Kravetz , Mike Rapoport , Pankaj Gupta , Baoquan He Subject: [PATCH v5 6/6] mm: document semantics of ZONE_MOVABLE Date: Sun, 16 Aug 2020 14:53:33 +0200 Message-Id: <20200816125333.7434-7-david@redhat.com> In-Reply-To: <20200816125333.7434-1-david@redhat.com> References: <20200816125333.7434-1-david@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Let's document what ZONE_MOVABLE means, how it's used, and which special cases we have regarding unmovable pages (memory offlining vs. migration / allocations). Acked-by: Mike Rapoport Cc: Andrew Morton Cc: Michal Hocko Cc: Michael S. Tsirkin Cc: Mike Kravetz Cc: Mike Rapoport Cc: Pankaj Gupta Cc: Baoquan He Signed-off-by: David Hildenbrand --- include/linux/mmzone.h | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index f6f884970511d..2456fcbaba152 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -372,6 +372,41 @@ enum zone_type { */ ZONE_HIGHMEM, #endif + /* + * ZONE_MOVABLE is similar to ZONE_NORMAL, except that it contains + * movable pages with few exceptional cases described below. Main use + * cases for ZONE_MOVABLE are to make memory offlining/unplug more + * likely to succeed, and to locally limit unmovable allocations - e.g., + * to increase the number of THP/huge pages. Notable special cases are: + * + * 1. Pinned pages: (long-term) pinning of movable pages might + * essentially turn such pages unmovable. Memory offlining might + * retry a long time. + * 2. memblock allocations: kernelcore/movablecore setups might create + * situations where ZONE_MOVABLE contains unmovable allocations + * after boot. Memory offlining and allocations fail early. + * 3. Memory holes: kernelcore/movablecore setups might create very rare + * situations where ZONE_MOVABLE contains memory holes after boot, + * for example, if we have sections that are only partially + * populated. Memory offlining and allocations fail early. + * 4. PG_hwpoison pages: while poisoned pages can be skipped during + * memory offlining, such pages cannot be allocated. + * 5. Unmovable PG_offline pages: in paravirtualized environments, + * hotplugged memory blocks might only partially be managed by the + * buddy (e.g., via XEN-balloon, Hyper-V balloon, virtio-mem). The + * parts not manged by the buddy are unmovable PG_offline pages. In + * some cases (virtio-mem), such pages can be skipped during + * memory offlining, however, cannot be moved/allocated. These + * techniques might use alloc_contig_range() to hide previously + * exposed pages from the buddy again (e.g., to implement some sort + * of memory unplug in virtio-mem). + * + * In general, no unmovable allocations that degrade memory offlining + * should end up in ZONE_MOVABLE. Allocators (like alloc_contig_range()) + * have to expect that migrating pages in ZONE_MOVABLE can fail (even + * if has_unmovable_pages() states that there are no unmovable pages, + * there can be false negatives). + */ ZONE_MOVABLE, #ifdef CONFIG_ZONE_DEVICE ZONE_DEVICE, -- 2.26.2