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=-8.4 required=3.0 tests=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,USER_AGENT_SANE_1 autolearn=ham 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 A5042C2D0B1 for ; Thu, 6 Feb 2020 10:00:49 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6625F20658 for ; Thu, 6 Feb 2020 10:00:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Cc0e7guC" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6625F20658 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id EDCC06B0003; Thu, 6 Feb 2020 05:00:48 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id E66056B0006; Thu, 6 Feb 2020 05:00:48 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D2DB16B0007; Thu, 6 Feb 2020 05:00:48 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0136.hostedemail.com [216.40.44.136]) by kanga.kvack.org (Postfix) with ESMTP id B66BA6B0003 for ; Thu, 6 Feb 2020 05:00:48 -0500 (EST) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 620AA8248D7C for ; Thu, 6 Feb 2020 10:00:48 +0000 (UTC) X-FDA: 76459258176.24.cat46_2411589238217 X-HE-Tag: cat46_2411589238217 X-Filterd-Recvd-Size: 5539 Received: from us-smtp-1.mimecast.com (us-smtp-delivery-1.mimecast.com [205.139.110.120]) by imf23.hostedemail.com (Postfix) with ESMTP for ; Thu, 6 Feb 2020 10:00:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1580983247; 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: in-reply-to:in-reply-to:references:references; bh=Sm/TORU59Zd8wltAgybpFtKimXAcKTN1yhP6FIGFtBg=; b=Cc0e7guC+riLLL0DDP7fw5edp/4gJR0fjxmPJdIpp2n/ur2vcML8qtGFujMMzjaNEH0wQH 3dazrxAeRXdP0gk/hMTK20bLPYRDXcqO3PmYA6YP7ztYhdD5AxlwuAm+3r5EMFXtN+q0kb i/Q7SF19+7qTKO9t3Eo9K4mPIlrVa5A= 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-370-00iuYu0nPAG9AT6tH0p76A-1; Thu, 06 Feb 2020 05:00:36 -0500 X-MC-Unique: 00iuYu0nPAG9AT6tH0p76A-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E03091034B21; Thu, 6 Feb 2020 10:00:34 +0000 (UTC) Received: from localhost (ovpn-12-19.pek2.redhat.com [10.72.12.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 371FE4FA9; Thu, 6 Feb 2020 10:00:31 +0000 (UTC) Date: Thu, 6 Feb 2020 18:00:29 +0800 From: Baoquan He To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, richardw.yang@linux.intel.com, mhocko@suse.com, osalvador@suse.de Subject: Re: [PATCH] mm/hotplug: Adjust shrink_zone_span() to keep the old logic Message-ID: <20200206100029.GP8965@MiWiFi-R3L-srv> References: <20200206053912.1211-1-bhe@redhat.com> <7ecaf36f-9f70-05bd-05fc-6dec82b7d559@redhat.com> <20200206093530.GO8965@MiWiFi-R3L-srv> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 02/06/20 at 10:48am, David Hildenbrand wrote: > On 06.02.20 10:35, Baoquan He wrote: > > On 02/06/20 at 09:50am, David Hildenbrand wrote: > >> On 06.02.20 06:39, Baoquan He wrote: > >>> In commit 950b68d9178b ("mm/memory_hotplug: don't check for "all holes" > >>> in shrink_zone_span()"), the zone->zone_start_pfn/->spanned_pages > >>> resetting is moved into the if()/else if() branches, if the zone becomes > >>> empty. However the 2nd resetting code block may cause misunderstanding. > >>> > >>> So take the resetting codes out of the conditional checking and handling > >>> branches just as the old code does, the find_smallest_section_pfn()and > >>> find_biggest_section_pfn() searching have done the the same thing as > >>> the old for loop did, the logic is kept the same as the old code. This > >>> can remove the possible confusion. > >>> > >>> Signed-off-by: Baoquan He > >>> --- > >>> mm/memory_hotplug.c | 14 ++++++-------- > >>> 1 file changed, 6 insertions(+), 8 deletions(-) > >>> > >>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > >>> index 089b6c826a9e..475d0d68a32c 100644 > >>> --- a/mm/memory_hotplug.c > >>> +++ b/mm/memory_hotplug.c > >>> @@ -398,7 +398,7 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone, > >>> static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, > >>> unsigned long end_pfn) > >>> { > >>> - unsigned long pfn; > >>> + unsigned long pfn = zone->zone_start_pfn; > >>> int nid = zone_to_nid(zone); > >>> > >>> zone_span_writelock(zone); > >>> @@ -414,9 +414,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, > >>> if (pfn) { > >>> zone->spanned_pages = zone_end_pfn(zone) - pfn; > >>> zone->zone_start_pfn = pfn; > >>> - } else { > >>> - zone->zone_start_pfn = 0; > >>> - zone->spanned_pages = 0; > >>> } > >>> } else if (zone_end_pfn(zone) == end_pfn) { > >>> /* > >>> @@ -429,10 +426,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, > >>> start_pfn); > >>> if (pfn) > >>> zone->spanned_pages = pfn - zone->zone_start_pfn + 1; > >>> - else { > >>> - zone->zone_start_pfn = 0; > >>> - zone->spanned_pages = 0; > >>> - } > >>> + } > >>> + > >>> + if (!pfn) { > >>> + zone->zone_start_pfn = 0; > >>> + zone->spanned_pages = 0; > >>> } > >>> zone_span_writeunlock(zone); > >>> } > >>> > >> > >> So, what if your zone starts at pfn 0? Unlikely that we can actually > >> offline that, but still it is more confusing than the old code IMHO. > >> Then I prefer to drop the second else case as discussed instead. > > > > Hmm, pfn is initialized as zone->zone_start_pfn, does it matter? > > The impossible empty zone won't go wrong if it really happen. > > > > If you offline any memory block that belongs to the lowest zone > (zone->zone_start_pfn == 0) but does not fall on a boundary (so that you > can actually shrink), you would mark the whole zone offline. That's > broken unless I am missing something. AFAIK, the page 0 is reserved. No valid zone can start at 0, only empty zone is. Please correct me if I am wrong.