From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 065A6362157 for ; Wed, 8 Apr 2026 07:36:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775633779; cv=none; b=qQrcYOK+RZSOY7R9apxkjePHKqV+TibHVk0fviznGSNxYr/v4QqOJXRnJneu+aX3HNUyOdR4IZuCIqGPu0UkXMwlZ2WUZYDMJ2vod+NXa//+zmXrB6S81taqK5LVBvmMdJevb7samF2PSjEYub47y0iuwfCpKR0OEo2nd3PF2YE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775633779; c=relaxed/simple; bh=9usUKozMxTM5/KPBGhFL/Q5Q+WRhnI82yaR3J4yHm9A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Jka8u4SV/N3f46D70K0me6vwz0Avau6j4B1gJ3RY/3+m1GxLoGKOzm3WKbW9tYFMSBdbBCdtsMz3uXmP5wjWn6afQ+++uyuy6PMclZpFPKxZ7KbdbgU6gPl1M9LBac1bb5Tf3stlvEp705n58i/wmJHQU40t+XZYJ0B3jFrvyJs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nBN6TY5G; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nBN6TY5G" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 358E3C2BCB0; Wed, 8 Apr 2026 07:36:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775633778; bh=9usUKozMxTM5/KPBGhFL/Q5Q+WRhnI82yaR3J4yHm9A=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=nBN6TY5GLLWEq3U7h/9ZirccALW3l4Tx4ivhOSx0sUKHGA1kyxKWjil3vxw8CK7gz yf2xzlKeYUJE2n/u08fy7XYLgX2ZBHpzeQxy4h0c77nWZVYQvDc6naZandP5Sw6m6b 8G9WHeVeNCxTVeT4FX7uNn7Ff1JEhX/9T6K2Kmmdy1CGD1Ku7FjSDuCwncxORKyg4e /9TiGZ/AxuGYiZ+i81To3jOOGzRkWUs7ybxqkYExRifwGqkjomQou1PqeXGRR4wtgE WMR1WF2XYtJeGlsYVfOrqTplvmhEXjc95oPGAu1xNYXtDNcmaTj3f229tLgjytv4L8 UI0J61zg01uaQ== Message-ID: <17b821b6-0176-43d5-92f7-fe2a0c4f70cf@kernel.org> Date: Wed, 8 Apr 2026 09:36:14 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/memory hotplug/unplug: Optimize zone contiguous check when changing pfn range To: Yuan Liu , Oscar Salvador , Mike Rapoport , Wei Yang Cc: linux-mm@kvack.org, Yong Hu , Nanhai Zou , Tim Chen , Qiuxu Zhuo , Yu C Chen , Pan Deng , Tianyou Li , Chen Zhang , linux-kernel@vger.kernel.org References: <20260408031615.1831922-1-yuan1.liu@intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/8/26 05:16, Yuan Liu wrote: > When move_pfn_range_to_zone() or remove_pfn_range_from_zone() updates a > zone, set_zone_contiguous() rescans the entire zone pageblock-by-pageblock > to rebuild zone->contiguous. For large zones this is a significant cost > during memory hotplug and hot-unplug. > > Add a new zone member pages_with_online_memmap that tracks the number of > pages within the zone span that have an online memory map (including present > pages and memory holes whose memory map has been initialized). When > spanned_pages == pages_with_online_memmap the zone is contiguous and > pfn_to_page() can be called on any PFN in the zone span without further > pfn_valid() checks. > > Only pages that fall within the current zone span are accounted towards > pages_with_online_memmap. A "too small" value is safe, it merely prevents > detecting a contiguous zone. > > The following test cases of memory hotplug for a VM [1], tested in the > environment [2], show that this optimization can significantly reduce the > memory hotplug time [3]. > > +----------------+------+---------------+--------------+----------------+ > | | Size | Time (before) | Time (after) | Time Reduction | > | +------+---------------+--------------+----------------+ > | Plug Memory | 256G | 10s | 3s | 70% | > | +------+---------------+--------------+----------------+ > | | 512G | 36s | 7s | 81% | > +----------------+------+---------------+--------------+----------------+ > > +----------------+------+---------------+--------------+----------------+ > | | Size | Time (before) | Time (after) | Time Reduction | > | +------+---------------+--------------+----------------+ > | Unplug Memory | 256G | 11s | 4s | 64% | > | +------+---------------+--------------+----------------+ > | | 512G | 36s | 9s | 75% | > +----------------+------+---------------+--------------+----------------+ > > [1] Qemu commands to hotplug 256G/512G memory for a VM: > object_add memory-backend-ram,id=hotmem0,size=256G/512G,share=on > device_add virtio-mem-pci,id=vmem1,memdev=hotmem0,bus=port1 > qom-set vmem1 requested-size 256G/512G (Plug Memory) > qom-set vmem1 requested-size 0G (Unplug Memory) > > [2] Hardware : Intel Icelake server > Guest Kernel : v7.0-rc4 > Qemu : v9.0.0 > > Launch VM : > qemu-system-x86_64 -accel kvm -cpu host \ > -drive file=./Centos10_cloud.qcow2,format=qcow2,if=virtio \ > -drive file=./seed.img,format=raw,if=virtio \ > -smp 3,cores=3,threads=1,sockets=1,maxcpus=3 \ > -m 2G,slots=10,maxmem=2052472M \ > -device pcie-root-port,id=port1,bus=pcie.0,slot=1,multifunction=on \ > -device pcie-root-port,id=port2,bus=pcie.0,slot=2 \ > -nographic -machine q35 \ > -nic user,hostfwd=tcp::3000-:22 > > Guest kernel auto-onlines newly added memory blocks: > echo online > /sys/devices/system/memory/auto_online_blocks > > [3] The time from typing the QEMU commands in [1] to when the output of > 'grep MemTotal /proc/meminfo' on Guest reflects that all hotplugged > memory is recognized. > > Reported-by: Nanhai Zou > Reported-by: Chen Zhang > Tested-by: Yuan Liu > Reviewed-by: Tim Chen > Reviewed-by: Qiuxu Zhuo > Reviewed-by: Yu C Chen > Reviewed-by: Pan Deng > Reviewed-by: Nanhai Zou > Co-developed-by: Tianyou Li > Signed-off-by: Tianyou Li > Signed-off-by: Yuan Liu > Acked-by: David Hildenbrand (Arm) > --- [...] > @@ -842,7 +842,7 @@ overlap_memmap_init(unsigned long zone, unsigned long *pfn) > * zone/node above the hole except for the trailing pages in the last > * section that will be appended to the zone/node below. > */ > -static void __init init_unavailable_range(unsigned long spfn, > +static unsigned long __init init_unavailable_range(unsigned long spfn, > unsigned long epfn, > int zone, int node) > { > @@ -858,6 +858,7 @@ static void __init init_unavailable_range(unsigned long spfn, > if (pgcnt) > pr_info("On node %d, zone %s: %lld pages in unavailable ranges\n", > node, zone_names[zone], pgcnt); > + return pgcnt; > } > > /* > @@ -956,9 +957,22 @@ static void __init memmap_init_zone_range(struct zone *zone, > memmap_init_range(end_pfn - start_pfn, nid, zone_id, start_pfn, > zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_MOVABLE, > false); > + zone->pages_with_online_memmap += end_pfn - start_pfn; > > - if (*hole_pfn < start_pfn) > - init_unavailable_range(*hole_pfn, start_pfn, zone_id, nid); > + if (*hole_pfn < start_pfn) { > + unsigned long pgcnt; > + > + if (*hole_pfn < zone_start_pfn) { > + init_unavailable_range(*hole_pfn, zone_start_pfn, > + zone_id, nid); > + pgcnt = init_unavailable_range(zone_start_pfn, > + start_pfn, zone_id, nid); Indentation of parameters. > + } else { > + pgcnt = init_unavailable_range(*hole_pfn, start_pfn, > + zone_id, nid); Same here. > + } > + zone->pages_with_online_memmap += pgcnt; > + } Maybe something like the following could make it nicer to read, just a thought. unsigned long hole_start_pfn = *hole_pfn; if (hole_start_pfn < zone_start_pfn) { init_unavailable_range(hole_start_pfn, zone_start_pfn, zone_id, nid); hole_start_pfn = zone_start_pfn; } pgcnt = init_unavailable_range(hole_start_pfn, start_pfn, zone_id, nid); LGTM, thanks! -- Cheers, David