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=-11.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 A15B7C433DB for ; Tue, 23 Feb 2021 10:09:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5067464E3F for ; Tue, 23 Feb 2021 10:09:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232440AbhBWKJE (ORCPT ); Tue, 23 Feb 2021 05:09:04 -0500 Received: from mail.kernel.org ([198.145.29.99]:55446 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232299AbhBWKHv (ORCPT ); Tue, 23 Feb 2021 05:07:51 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id BA91864E3F; Tue, 23 Feb 2021 10:07:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1614074830; bh=ldsGlNDSWjObH//AcaVyVQQKhLO6Y4NGrLkEEk/X1Fw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=RbK9+nibc62xkE6KYKhOYU2/DAkFZdXP5FAppKjVSO6+bAQ8rT49E2p0xz70sCeKg CanSZRBIKjopRCmoFauqzMQO0ahgfBqdp8OLhf0HTOKAW81Nxdxkhmue1lA1H/BzZR E1j2euU99oiLWUta8OltH4Yb/me+UivaK/b5Z8anO04LeWlMlYBTyz7lCOQHlMLBZC 0w5Zuterro0K5aVcTIJMfrcLBv3ADFpNNDGovuYZjU8s5chhvSmiIX9eDYtKhoYAxY ywKIbb4g9ghAeaVChMmr7wxqQ1MGUc+a6/2DforsrqiCRDlnPOkdIUtmDFFHn1dJWs jbbpF1r2ITpww== Date: Tue, 23 Feb 2021 12:06:59 +0200 From: Mike Rapoport To: David Hildenbrand Cc: Andrew Morton , Andrea Arcangeli , Baoquan He , Borislav Petkov , Chris Wilson , "H. Peter Anvin" , Ingo Molnar , Linus Torvalds , =?utf-8?Q?=C5=81ukasz?= Majczak , Mel Gorman , Michal Hocko , Mike Rapoport , Qian Cai , "Sarvela, Tomi P" , Thomas Gleixner , Vlastimil Babka , linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH v6 1/1] mm/page_alloc.c: refactor initialization of struct page for holes in memory layout Message-ID: <20210223100659.GJ1447004@kernel.org> References: <20210222105728.28636-1-rppt@kernel.org> <20210223094802.GI1447004@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 23, 2021 at 10:49:44AM +0100, David Hildenbrand wrote: > On 23.02.21 10:48, Mike Rapoport wrote: > > On Tue, Feb 23, 2021 at 09:04:19AM +0100, David Hildenbrand wrote: > > > On 22.02.21 11:57, Mike Rapoport wrote: > > > > From: Mike Rapoport > > > > > > > > There could be struct pages that are not backed by actual physical memory. > > > > This can happen when the actual memory bank is not a multiple of > > > > SECTION_SIZE or when an architecture does not register memory holes > > > > reserved by the firmware as memblock.memory. > > > > > > > > Such pages are currently initialized using init_unavailable_mem() function > > > > that iterates through PFNs in holes in memblock.memory and if there is a > > > > struct page corresponding to a PFN, the fields of this page are set to > > > > default values and it is marked as Reserved. > > > > > > > > init_unavailable_mem() does not take into account zone and node the page > > > > belongs to and sets both zone and node links in struct page to zero. > > > > > > > > Before commit 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions > > > > rather that check each PFN") the holes inside a zone were re-initialized > > > > during memmap_init() and got their zone/node links right. However, after > > > > that commit nothing updates the struct pages representing such holes. > > > > > > > > On a system that has firmware reserved holes in a zone above ZONE_DMA, for > > > > instance in a configuration below: > > > > > > > > # grep -A1 E820 /proc/iomem > > > > 7a17b000-7a216fff : Unknown E820 type > > > > 7a217000-7bffffff : System RAM > > > > > > > > unset zone link in struct page will trigger > > > > > > > > VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page); > > > > > > > > because there are pages in both ZONE_DMA32 and ZONE_DMA (unset zone link > > > > in struct page) in the same pageblock. > > > > > > > > Interleave initialization of the unavailable pages with the normal > > > > initialization of memory map, so that zone and node information will be > > > > properly set on struct pages that are not backed by the actual memory. > > > > > > > > With this change the pages for holes inside a zone will get proper > > > > zone/node links and the pages that are not spanned by any node will get > > > > links to the adjacent zone/node. > > > > > > Does this include pages in the last section has handled by ... > > > ... > > > > - /* > > > > - * Early sections always have a fully populated memmap for the whole > > > > - * section - see pfn_valid(). If the last section has holes at the > > > > - * end and that section is marked "online", the memmap will be > > > > - * considered initialized. Make sure that memmap has a well defined > > > > - * state. > > > > - */ > > > > - pgcnt += init_unavailable_range(PFN_DOWN(next), > > > > - round_up(max_pfn, PAGES_PER_SECTION)); > > > > - > > > > > > ^ this code? > > > > > > Or how is that case handled now? > > > > Hmm, now it's clamped to node_end_pfn/zone_end_pfn, so in your funny example with > > > > -object memory-backend-ram,id=bmem0,size=4160M \ > > -object memory-backend-ram,id=bmem1,size=4032M \ > > > > this is not handled :( > > > > But it will be handled with this on top: > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 29bbd08b8e63..6c9b490f5a8b 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -6350,9 +6350,12 @@ void __meminit __weak memmap_init_zone(struct zone *zone) > > hole_pfn = end_pfn; > > } > > - if (hole_pfn < zone_end_pfn) > > - pgcnt += init_unavailable_range(hole_pfn, zone_end_pfn, > > +#ifdef CONFIG_SPARSEMEM > > + end_pfn = round_up(zone_end_pfn, PAGES_PER_SECTION); > > + if (hole_pfn < end_pfn) > > + pgcnt += init_unavailable_range(hole_pfn, end_pfn, > > zone_id, nid); > > +#endif > > if (pgcnt) > > pr_info(" %s zone: %lld pages in unavailable ranges\n", > > > > > Also, just wondering, will PFN 0 still get initialized? Yes, it gets 0,0 links, but it is still outside node/zone span. -- Sincerely yours, Mike.