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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 9695AC2D0E4 for ; Fri, 27 Nov 2020 15:03:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3AD9B22240 for ; Fri, 27 Nov 2020 15:03:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="AsYyALuX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731138AbgK0PCz (ORCPT ); Fri, 27 Nov 2020 10:02:55 -0500 Received: from mx2.suse.de ([195.135.220.15]:54808 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729913AbgK0PCy (ORCPT ); Fri, 27 Nov 2020 10:02:54 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1606489373; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=v4TKnwpt34GOmnbBGpsXCxPVfzwSqU1ksAh0rwDzx+k=; b=AsYyALuXVEpBKUehNq+bcdmyFn/XAyfhDkDi0xWI25WqWNoJLZ1VOnWQOXvHq2TBjPJ07c n2286ROf/HNZRh2C+cnzPJsAp0ayf8JB/NPBcwIKHBr1HtOn4YsRVvdnXHqA95NCBBn5ey IsTwKBHRZTGg2tcVkkIW8czk6tSVMgw= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id B7E48ACBF; Fri, 27 Nov 2020 15:02:53 +0000 (UTC) Date: Fri, 27 Nov 2020 16:02:53 +0100 From: Michal Hocko To: Oscar Salvador Cc: david@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, vbabka@suse.cz, pasha.tatashin@soleen.com Subject: Re: [RFC PATCH v2 3/4] mm,memory_hotplug: Add mhp_supports_memmap_on_memory Message-ID: <20201127150253.GU31550@dhcp22.suse.cz> References: <20201125112048.8211-1-osalvador@suse.de> <20201125112048.8211-4-osalvador@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201125112048.8211-4-osalvador@suse.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 25-11-20 12:20:47, Oscar Salvador wrote: > mhp_supports_memmap_on_memory is meant to be used by the caller prior > to hot-adding memory in order to figure out whether it can enable > MHP_MEMMAP_ON_MEMORY or not. > > Enabling MHP_MEMMAP_ON_MEMORY requires: > > - CONFIG_SPARSEMEM_VMEMMAP > - architecture support for altmap > - hot-added range spans a single memory block It should also require a tunable (kernel parameter for now but maybe we will need a more fine grained control later) to enable this explicitly. Earlier discussions have pointed out that allocating vmemmap from each section can lead to a sparse memory unsuitable for very large pages. So I believe this should be an opt in. Also is there any reason why this cannot be a preparatory patch for the actual implementation? It would look more natural that way to me. -- Michal Hocko SUSE Labs