From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 EB0C43D647C for ; Wed, 5 Aug 2026 11:02:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785927755; cv=none; b=rMuYHYvqBmkwdY502zIuV+TbUjl46wgJPlBf3Bg3da8IhOgH/ZXFcdndY+H5eQL/W1IzV7mWr0DOgKcYHdgteDzGuyd0G2KfhPEwhfKIv1mIYIGLcJFSaRHNMg9Lx3z12WJ7PxlLpg6D2ElTsZ9YyCLFLzD+sycx1MckTWM/rtY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785927755; c=relaxed/simple; bh=84PniVYmQuOdm8J7ehelZClgkf5J2CNVWY5YG28Ai28=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ppT8VahmCWlaqdh+3VBWvmQZLlOEAp589jiXohwOFXfYTcwJADaNpJdLv6vmNeXqILQWU8wqEZU52LS7G6ihdlhExxRMq+S7t2MSVrXJpcr/xS+GoJnKbjKWwWy2YmxuXL72A3E6lsCK5Lm7sNifipimCEn/+XNkTVl+lFpmPeQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=a2OG/14D; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="a2OG/14D" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 11DF11F000E9; Wed, 5 Aug 2026 11:02:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785927753; bh=pLxE5qUs1sNIGK998MMucs9/LacSHU2wxGh+jo5l8SM=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=a2OG/14DcRTRu37pq6vQtM+Ca5YodwL3Gyv6J3KV7GReTPPQt8gGM9X5001+xQez+ DZwzk2QdEBoKC3jm8wuAKv3soQp7qZsBGL3slKAZ/6dUi02loloY8JHFqdPzgPuGhO iGM6z6Nk4I38djrfSrrZOZPZGwPOp0nSNfATLFzjyNb0+i0iWpeNGviGCdYUQL8K47 kBYntJmsXQuXce+u39g70sKihTaOor7Iu6V4UrRdhQ/mUMOto+w58TZb3kD/2d4bZi r22qCVGF/vLWpB9Vx/6m5dw+JPy06gigeRpKtvQX87m1HqcPbQNl+vR230oy5thyK1 hW6YHUY9oCnIA== Message-ID: Date: Wed, 5 Aug 2026 13:02:29 +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 v6 2/2] mm/memory_hotplug: improve shrink_zone_span() subsection boundary checks To: Yuan Liu , Oscar Salvador , Mike Rapoport , Wei Yang Cc: linux-mm@kvack.org, Nanhai Zou , Pan Deng , Tianyou Li , Chen Zhang , Jason Zeng , linux-kernel@vger.kernel.org References: <20260723084946.189392-1-yuan1.liu@intel.com> <20260723084946.189392-3-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 7/23/26 10:49, Yuan Liu wrote: > When shrinking a zone span after removing a PFN range, > find_smallest_section_pfn() and find_biggest_section_pfn() > only checked one edge PFN in each subsection for nid/zone matching. > > If a memory or hole boundary falls in the middle of a subsection, > that edge PFN may belong to a different nid/zone, causing the helpers > to miss a valid PFN within that subsection. > > Fix this by checking both subsection edge PFNs for nid/zone matching. > Keep a single pfn_to_online_page() check per subsection, since online > state is the same for all PFNs in a subsection. > > Reviewed-by: Jason Zeng > Signed-off-by: Yuan Liu > --- > mm/memory_hotplug.c | 42 +++++++++++++++++++++++++++--------------- > 1 file changed, 27 insertions(+), 15 deletions(-) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 4c699fd9c479..3a281d595207 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -427,17 +427,24 @@ static unsigned long find_smallest_section_pfn(int nid, struct zone *zone, > unsigned long start_pfn, > unsigned long end_pfn) > { > - for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUBSECTION) { > - if (unlikely(!pfn_to_online_page(start_pfn))) > - continue; > + unsigned long next_pfn; > > - if (unlikely(pfn_to_nid(start_pfn) != nid)) > - continue; > + for (; start_pfn < end_pfn; start_pfn = next_pfn) { > + unsigned long tail_pfn; > > - if (zone != page_zone(pfn_to_page(start_pfn))) > + next_pfn = start_pfn + PAGES_PER_SUBSECTION; > + tail_pfn = next_pfn - 1; > + > + if (unlikely(!pfn_to_online_page(start_pfn))) > continue; > > - return start_pfn; > + if (likely(pfn_to_nid(start_pfn) == nid) && > + zone == page_zone(pfn_to_page(start_pfn))) > + return start_pfn; > + > + if (likely(pfn_to_nid(tail_pfn) == nid) && > + zone == page_zone(pfn_to_page(tail_pfn))) > + return start_pfn; > } > > return 0; > @@ -448,21 +455,26 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone, > unsigned long start_pfn, > unsigned long end_pfn) > { > - unsigned long pfn; > + unsigned long pfn, prev_pfn; > > /* pfn is the end pfn of a memory section. */ > pfn = end_pfn - 1; > - for (; pfn >= start_pfn; pfn -= PAGES_PER_SUBSECTION) { > - if (unlikely(!pfn_to_online_page(pfn))) > - continue; > + for (; pfn >= start_pfn; pfn = prev_pfn) { > + unsigned long head_pfn; > > - if (unlikely(pfn_to_nid(pfn) != nid)) > - continue; > + prev_pfn = pfn - PAGES_PER_SUBSECTION; > + head_pfn = prev_pfn + 1; > > - if (zone != page_zone(pfn_to_page(pfn))) > + if (unlikely(!pfn_to_online_page(pfn))) > continue; > > - return pfn; > + if (likely(pfn_to_nid(pfn) == nid) && > + zone == page_zone(pfn_to_page(pfn))) > + return pfn; > + > + if (likely(pfn_to_nid(head_pfn) == nid) && > + zone == page_zone(pfn_to_page(head_pfn))) > + return pfn; > } > > return 0; I think improving that should be patch #1. But I think we can do much better code-wise. What about the following cleanup instead: >From 6e9ea094daf8d04c0b119b780572a846334f8164 Mon Sep 17 00:00:00 2001 From: "David Hildenbrand (Arm)" Date: Wed, 5 Aug 2026 12:52:55 +0200 Subject: [PATCH] mm/memory_hotplug: make shrink_zone_span() more robust Let's make shrink_zone_span() more robust by checking in find_smallest_section_pfn() / find_biggest_section_pfn() that start+end of the subsection. While at it, clean up the function heavily, factoring the core check out into subsection_overlaps_zone(). There likely is no need to check for the nid first: we require SPARSEMEM_VMEMMAP_ENABLE where pfn_to_page() is cheap, and the pfn_to_nid() on CONFIG_NUMA would do a pfn_to_page() either way. So let's just drop that for now. Signed-off-by: David Hildenbrand (Arm) --- mm/memory_hotplug.c | 59 ++++++++++++++++++--------------------------- 1 file changed, 24 insertions(+), 35 deletions(-) diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 226ab9cb078ad..79937f9672d01 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -425,49 +425,39 @@ int __add_pages(int nid, unsigned long pfn, unsigned long nr_pages, return err; } -/* find the smallest valid pfn in the range [start_pfn, end_pfn) */ -static unsigned long find_smallest_section_pfn(int nid, struct zone *zone, - unsigned long start_pfn, - unsigned long end_pfn) +static bool subsection_overlaps_zone(unsigned long pfn, struct zone *zone) { - for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUBSECTION) { - if (unlikely(!pfn_to_online_page(start_pfn))) - continue; + const unsigned long start_pfn = ALIGN_DOWN(pfn, PAGES_PER_SUBSECTION); + const unsigned long end_pfn = start_pfn + PAGES_PER_SUBSECTION - 1; - if (unlikely(pfn_to_nid(start_pfn) != nid)) - continue; + /* All pages in a subsection are either online or offline. */ + if (unlikely(!pfn_to_online_page(start_pfn))) + return false; - if (zone != page_zone(pfn_to_page(start_pfn))) - continue; + /* Checking start+end is sufficient. */ + return zone == page_zone(pfn_to_page(start_pfn)) || + zone == page_zone(pfn_to_page(end_pfn)); +} - return start_pfn; +/* find the smallest valid pfn in the range [start_pfn, end_pfn) */ +static unsigned long find_smallest_section_pfn(struct zone *zone, + unsigned long start_pfn, unsigned long end_pfn) +{ + for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUBSECTION) { + if (subsection_overlaps_zone(start_pfn, zone)) + return start_pfn; } - return 0; } /* find the biggest valid pfn in the range [start_pfn, end_pfn). */ -static unsigned long find_biggest_section_pfn(int nid, struct zone *zone, - unsigned long start_pfn, - unsigned long end_pfn) +static unsigned long find_biggest_section_pfn(struct zone *zone, + unsigned long start_pfn, unsigned long end_pfn) { - unsigned long pfn; - - /* pfn is the end pfn of a memory section. */ - pfn = end_pfn - 1; - for (; pfn >= start_pfn; pfn -= PAGES_PER_SUBSECTION) { - if (unlikely(!pfn_to_online_page(pfn))) - continue; - - if (unlikely(pfn_to_nid(pfn) != nid)) - continue; - - if (zone != page_zone(pfn_to_page(pfn))) - continue; - - return pfn; + for (; end_pfn >= start_pfn; end_pfn -= PAGES_PER_SUBSECTION) { + if (subsection_overlaps_zone(end_pfn - 1, zone)) + return end_pfn - 1; } - return 0; } @@ -475,7 +465,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, unsigned long end_pfn) { unsigned long pfn; - int nid = zone_to_nid(zone); if (zone->zone_start_pfn == start_pfn) { /* @@ -484,7 +473,7 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, * In this case, we find second smallest valid mem_section * for shrinking zone. */ - pfn = find_smallest_section_pfn(nid, zone, end_pfn, + pfn = find_smallest_section_pfn(zone, end_pfn, zone_end_pfn(zone)); if (pfn) { zone->spanned_pages = zone_end_pfn(zone) - pfn; @@ -500,7 +489,7 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, * In this case, we find second biggest valid mem_section for * shrinking zone. */ - pfn = find_biggest_section_pfn(nid, zone, zone->zone_start_pfn, + pfn = find_biggest_section_pfn(zone, zone->zone_start_pfn, start_pfn); if (pfn) zone->spanned_pages = pfn - zone->zone_start_pfn + 1; -- 2.43.0 -- Cheers, David