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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 5C935FA3728 for ; Wed, 16 Oct 2019 11:20:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 36AEA2168B for ; Wed, 16 Oct 2019 11:20:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571224856; bh=doIzJeXQHVjz1M7XJVXHJuv2iUQRkWCgC9w9YrOIaAU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=JpQ8RC5xpd+1mnUxQsF5W/86JrK7osiae2nMnYi8hu6SMk6r8ziTKMLYuIHfdAEWp vbBsMooMlPcRsEwguOS3aCvbdTGKZglgvppb5Fq20skDq+EYQ0CsydukkLs2shwk7d u+n0UHiONe48ZI0hhGCzBagR2rmrg3n+lIM2CPS8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392703AbfJPLUz (ORCPT ); Wed, 16 Oct 2019 07:20:55 -0400 Received: from mx2.suse.de ([195.135.220.15]:57446 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728406AbfJPLUy (ORCPT ); Wed, 16 Oct 2019 07:20:54 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id BF6F0B304; Wed, 16 Oct 2019 11:20:52 +0000 (UTC) Date: Wed, 16 Oct 2019 13:20:51 +0200 From: Michal Hocko To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, virtualization@lists.linux-foundation.org, Andrea Arcangeli , Andrew Morton , Vlastimil Babka , Oscar Salvador , Mel Gorman , Mike Rapoport , Dan Williams , Alexander Duyck , Pavel Tatashin , Alexander Potapenko Subject: Re: [PATCH RFC v3 4/9] mm: Export alloc_contig_range() / free_contig_range() Message-ID: <20191016112051.GW317@dhcp22.suse.cz> References: <20190919142228.5483-1-david@redhat.com> <20190919142228.5483-5-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190919142228.5483-5-david@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 19-09-19 16:22:23, David Hildenbrand wrote: > A virtio-mem device wants to allocate memory from the memory region it > manages in order to unplug it in the hypervisor - similar to > a balloon driver. Also, it might want to plug previously unplugged > (allocated) memory and give it back to Linux. alloc_contig_range() / > free_contig_range() seem to be the perfect interface for this task. > > In contrast to existing balloon devices, a virtio-mem device operates > on bigger chunks (e.g., 4MB) and only on physical memory it manages. It > tracks which chunks (subblocks) are still plugged, so it can go ahead > and try to alloc_contig_range()+unplug them on unplug request, or > plug+free_contig_range() unplugged chunks on plug requests. > > A virtio-mem device will use alloc_contig_range() / free_contig_range() > only on ranges that belong to the same node/zone in at least > MAX(MAX_ORDER - 1, pageblock_order) order granularity - e.g., 4MB on > x86-64. The virtio-mem device added that memory, so the memory > exists and does not contain any holes. virtio-mem will only try to allocate > on ZONE_NORMAL, never on ZONE_MOVABLE, just like when allocating > gigantic pages (we don't put unmovable data into the movable zone). Is there any real reason to export as GPL rather than generic EXPORT_SYMBOL? In other words do we need to restrict the usage this interface only to GPL modules and why if so. All other allocator APIs are EXPORT_SYMBOL so there should better be a good reason for this one to differ. I can understand that this one is slightly different by requesting a specific range of the memory but it is still under a full control of the core MM to say no. > Cc: Andrew Morton > Cc: Michal Hocko > Cc: Vlastimil Babka > Cc: Oscar Salvador > Cc: Mel Gorman > Cc: Mike Rapoport > Cc: Dan Williams > Cc: Alexander Duyck > Cc: Pavel Tatashin > Cc: Alexander Potapenko > Signed-off-by: David Hildenbrand Other than that, I do not think exporting this function is harmful. It would be worse to reinvent it and do it wrong. I usually prefer to add a caller in the same patch, though, because it makes the usage explicit and clear. Acked-by: Michal Hocko # to export contig range allocator API > --- > mm/page_alloc.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3334a769eb91..d5d7944954b3 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -8469,6 +8469,7 @@ int alloc_contig_range(unsigned long start, unsigned long end, > pfn_max_align_up(end), migratetype); > return ret; > } > +EXPORT_SYMBOL_GPL(alloc_contig_range); > #endif /* CONFIG_CONTIG_ALLOC */ > > void free_contig_range(unsigned long pfn, unsigned int nr_pages) > @@ -8483,6 +8484,7 @@ void free_contig_range(unsigned long pfn, unsigned int nr_pages) > } > WARN(count != 0, "%d pages are still in use!\n", count); > } > +EXPORT_SYMBOL_GPL(free_contig_range); > > #ifdef CONFIG_MEMORY_HOTPLUG > /* > -- > 2.21.0 -- Michal Hocko SUSE Labs