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 280AD3009F6 for ; Mon, 23 Mar 2026 11:42:23 +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=1774266144; cv=none; b=kTUN2xlFCSD/yRJ1MW82UIpKcvcfnHzyX00RXivOusuCmUT5CUwnQdl1fImQ4kOlMgAysbwPOVpzhB802aUD+q6FhQgy9RKINxJGLcZ0tOp09jZ6vGqQD6GnJ3JtwNMa9DOcSkVl170AysbUKJEeWL1wKO8PHiYUy73ApPtmjv8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774266144; c=relaxed/simple; bh=dLC6SP4EM8xLyJEG0yB5l0xv9xeTKuqp/PvgzfJWfF0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=crg+wFQw2ZikEUtrSYCLNB+peNToS2dFVL8OzQUrr0i8J+wJ00EBjFaF9PH9gZv6TvAlDsry99+G9lLh67uOj748SMwB9NUinwMqTvpZvicylJQMYczQC/OFgms0O2AB2MoD357EnTx0pOcz+HR+GPe5M3Mh/DWgg7su4IGvlO0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=A9e8/8wO; 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="A9e8/8wO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E6D5FC2BCB1; Mon, 23 Mar 2026 11:42:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774266143; bh=dLC6SP4EM8xLyJEG0yB5l0xv9xeTKuqp/PvgzfJWfF0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=A9e8/8wOYSIqy2CuuHmLMO9krzNDhF/9QpdvGobrrU2Y1p2BR3w/CClxvbK+JcTTP YslIsieMvOC+1vGTS8nyZdxuwbf/fjpfVLv9I5yTeK51ZXwshnrKF/eFR3vPeXqQov seAWXDB8j0cCMtI9Gyf8SYIgw/rcnFWYhQXKNBYmQCzb68ueM9Y2VRV9pliaxbhR7m +zvItDY8dxcWqWlNVmSGcgrmV/zXM7OcXycOaEfqE7JI5SWGFjOQiWmL2vz8dUiKkO Pk54PopJr50UAeIe357yB+Pd45RyxiorUWBhb3wv/4hTVUdnARrF4OIAfxg8nzbGr3 ieZAR4Af0raAA== Message-ID: <168ab3c0-c44f-4d48-b7dc-33196b7ba6a5@kernel.org> Date: Mon, 23 Mar 2026 12:42:18 +0100 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] mm/memory hotplug/unplug: Optimize zone contiguous check when changing pfn range To: Mike Rapoport Cc: Yuan Liu , Oscar Salvador , Wei Yang , 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: <20260319095622.1130380-1-yuan1.liu@intel.com> <48b497e5-1545-4376-a898-f3813a6ef989@kernel.org> 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 3/23/26 12:31, Mike Rapoport wrote: > On Mon, Mar 23, 2026 at 11:56:35AM +0100, David Hildenbrand (Arm) wrote: >> On 3/19/26 10:56, Yuan Liu wrote: > > ... > >>> diff --git a/mm/mm_init.c b/mm/mm_init.c >>> index df34797691bd..96690e550024 100644 >>> --- a/mm/mm_init.c >>> +++ b/mm/mm_init.c >>> @@ -946,6 +946,7 @@ static void __init memmap_init_zone_range(struct zone *zone, >>> unsigned long zone_start_pfn = zone->zone_start_pfn; >>> unsigned long zone_end_pfn = zone_start_pfn + zone->spanned_pages; >>> int nid = zone_to_nid(zone), zone_id = zone_idx(zone); >>> + unsigned long zone_hole_start, zone_hole_end; >>> >>> start_pfn = clamp(start_pfn, zone_start_pfn, zone_end_pfn); >>> end_pfn = clamp(end_pfn, zone_start_pfn, zone_end_pfn); >>> @@ -957,8 +958,19 @@ static void __init memmap_init_zone_range(struct zone *zone, >>> zone_end_pfn, MEMINIT_EARLY, NULL, MIGRATE_MOVABLE, >>> false); >>> >>> - if (*hole_pfn < start_pfn) >>> + WRITE_ONCE(zone->pages_with_online_memmap, >>> + READ_ONCE(zone->pages_with_online_memmap) + >>> + (end_pfn - start_pfn)); >>> + >>> + if (*hole_pfn < start_pfn) { >>> init_unavailable_range(*hole_pfn, start_pfn, zone_id, nid); >>> + zone_hole_start = clamp(*hole_pfn, zone_start_pfn, zone_end_pfn); >>> + zone_hole_end = clamp(start_pfn, zone_start_pfn, zone_end_pfn); >>> + if (zone_hole_start < zone_hole_end) >>> + WRITE_ONCE(zone->pages_with_online_memmap, >>> + READ_ONCE(zone->pages_with_online_memmap) + >>> + (zone_hole_end - zone_hole_start)); >>> + } >> >> The range can have larger holes without a memmap, and I think we would be >> missing pages handled by the other init_unavailable_range() call? >> >> >> There is one question for Mike, though: couldn't it happen that the >> init_unavailable_range() call in memmap_init() would initialize >> the memmap outside of the node/zone span? > > Yes, and it most likely will. > > Very common example is page 0 on x86 systems: > > [ 0.012196] DMA [mem 0x0000000000001000-0x0000000000ffffff] > [ 0.012221] On node 0, zone DMA: 1 pages in unavailable ranges > [ 0.012205] Early memory node ranges > [ 0.012206] node 0: [mem 0x0000000000001000-0x000000000009efff] > > The unavailable page in zone DMA is the page from 0x0 to 0x1000 that is > neither in node 0 nor in zone DMA. > > For ZONE_NORMAL it would be a more pathological case when zone/node span > ends in a middle of a section, but that's still possible. > >> If so, I wonder whether we would want to adjust the node+zone space to >> include these ranges. >> >> Later memory onlining could make these ranges suddenly fall into the >> node/zone span. > > But doesn't memory onlining always happen at section boundaries? Sure, but assume ZONE_NORMAL ends in the middle of a section, and then you hotplug the next section. Then, the zone spans that memmap. zone->pages_with_online_memmap will be wrong. Once we unplug the hotplugged section, zone shrinking code will stumble over the whole-pfns and assume they belong to the zone. zone->pages_with_online_memmap will be wrong. zone->pages_with_online_memmap being wrong means that it is smaller than it should. I guess, it would not be broken, but we would fail to detect contiguous zones. If there would be an easy way to avoid that, that would be cleaner. -- Cheers, David