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 31390C2D0B1 for ; Thu, 6 Feb 2020 09:35:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id DB9D720720 for ; Thu, 6 Feb 2020 09:35:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="R2LQcvcf" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DB9D720720 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 726BE6B0003; Thu, 6 Feb 2020 04:35:43 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 6D7096B0006; Thu, 6 Feb 2020 04:35:43 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5C52D6B0007; Thu, 6 Feb 2020 04:35:43 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0146.hostedemail.com [216.40.44.146]) by kanga.kvack.org (Postfix) with ESMTP id 41A5F6B0003 for ; Thu, 6 Feb 2020 04:35:43 -0500 (EST) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id D06B3180AD802 for ; Thu, 6 Feb 2020 09:35:42 +0000 (UTC) X-FDA: 76459194924.05.arm45_6c0b40122422f X-HE-Tag: arm45_6c0b40122422f X-Filterd-Recvd-Size: 4834 Received: from us-smtp-delivery-1.mimecast.com (us-smtp-2.mimecast.com [207.211.31.81]) by imf47.hostedemail.com (Postfix) with ESMTP for ; Thu, 6 Feb 2020 09:35:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1580981742; 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=GQ1cUTREQNuJAu5bUl8Fv+OR09amMOpiErx1l97ZOCA=; b=R2LQcvcffXcLT5VQX76lNJAOPL1NvOLawRezzeWqgpd1bwIWRQ+o95SjKTTPVCtYAbY/pH QIzU2oRCs1/DoVBG7TjJQWE+GA0GGVTti+tFPVu5IC08plq4uTVGGzn4HpskY8Efg3PZki B4ibNmUgb1crXrwVy4CXsnU5FAlX+6U= 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-113-GWDkqie6OSu9-T2rBII9QA-1; Thu, 06 Feb 2020 04:35:38 -0500 X-MC-Unique: GWDkqie6OSu9-T2rBII9QA-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 B918418A6EC0; Thu, 6 Feb 2020 09:35:36 +0000 (UTC) Received: from localhost (ovpn-12-19.pek2.redhat.com [10.72.12.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2089D1A8E4; Thu, 6 Feb 2020 09:35:33 +0000 (UTC) Date: Thu, 6 Feb 2020 17:35:30 +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: <20200206093530.GO8965@MiWiFi-R3L-srv> References: <20200206053912.1211-1-bhe@redhat.com> <7ecaf36f-9f70-05bd-05fc-6dec82b7d559@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7ecaf36f-9f70-05bd-05fc-6dec82b7d559@redhat.com> 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 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.