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 30EC823B615 for ; Mon, 1 Dec 2025 18:54:40 +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=1764615281; cv=none; b=qCsPXqJmZtkemSgth3Ewil3dIC/bKVHvjMUN/O8b5pZKahgCCLZbW+uMuDjecNpdnUf7Yl1eJMwsPfefBKzKjJHXtqXCBat8eANNADGaU808lEKQ8k2uHTrlEG3l4T2FACdwyq0bwUGcFDkfK9Gd+nvxY620Z+uLnhMcPiia8a8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764615281; c=relaxed/simple; bh=1q3jskg7gK0OTAOEWa2SXDK5o1qCYd761gFxc0pcLdM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=DVMZPe4fVMkyTjXaQnZiv8eWRwY2ntjG9YaH0CsFbSrctvWFDnWNZMb3S6rvUn2rBRnMYCbJGwAYkkehMSJzOhR32BYQPxhh7eMkBjI8rWF310x0uJ5DyHmPgULHwUzX9oBKFqI6V5bpiMg7LRfzIQJRn/DW3yd3wAErid0oOP4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pnWWPZ6w; 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="pnWWPZ6w" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E6C69C116C6; Mon, 1 Dec 2025 18:54:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764615280; bh=1q3jskg7gK0OTAOEWa2SXDK5o1qCYd761gFxc0pcLdM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=pnWWPZ6wjIQcVWY2jrPUogtwKylkMrX+ngJIuCPW6vH2Y8i4OtThTnLGilWvkxjk5 MJENeHOh57IOLCmn2Zo6TSirMhTsI1xeOl+YTT0J0P0WORaiJQCXDOKRZnHJjE5AQg AyHLZ9okUVUWNX62zRbvxHa3G+e6Fdqxddwsh25RtsulKRlgWZjr7gpPOFfkfVaQUK SemuJrkVA7PJYJ4nEsrlGowXYhiNIaMDXb8rjSHYk/O82RF0pmv3lodAzZDpP4+DKR c0sVaXfq5YOdpkDKeUqn8WPb+4VVULkvS9oGzj0ftAd4h/Ep5V/WA21q7mSMCmXUov Y7CgcRnJ4oE9Q== Message-ID: <7633c77b-44eb-41f0-9c3a-1e5034b594e3@kernel.org> Date: Mon, 1 Dec 2025 19:54:34 +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 v4] mm/memory hotplug/unplug: Optimize zone->contiguous update when changes pfn range To: Tianyou Li , Oscar Salvador , Mike Rapoport , Wei Yang Cc: linux-mm@kvack.org, Yong Hu , Nanhai Zou , Yuan Liu , Tim Chen , Qiuxu Zhuo , Yu C Chen , Pan Deng , Chen Zhang , linux-kernel@vger.kernel.org References: <20251201132216.1636924-1-tianyou.li@intel.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <20251201132216.1636924-1-tianyou.li@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12/1/25 14:22, Tianyou Li wrote: > When invoke move_pfn_range_to_zone or remove_pfn_range_from_zone, it will > update the zone->contiguous by checking the new zone's pfn range from the > beginning to the end, regardless the previous state of the old zone. When > the zone's pfn range is large, the cost of traversing the pfn range to > update the zone->contiguous could be significant. > > Add fast paths to quickly detect cases where zone is definitely not > contiguous without scanning the new zone. The cases are: when the new range > did not overlap with previous range, the contiguous should be false; if the > new range adjacent with the previous range, just need to check the new > range; if the new added pages could not fill the hole of previous zone, the > contiguous should be false. > > 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 | 2s | 80% | > | +------+---------------+--------------+----------------+ > | | 512G | 33s | 6s | 81% | > +----------------+------+---------------+--------------+----------------+ > > +----------------+------+---------------+--------------+----------------+ > | | Size | Time (before) | Time (after) | Time Reduction | > | +------+---------------+--------------+----------------+ > | Unplug Memory | 256G | 10s | 2s | 80% | > | +------+---------------+--------------+----------------+ > | | 512G | 34s | 6s | 82% | > +----------------+------+---------------+--------------+----------------+ > > [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 : v6.18-rc2 > 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 > Reviewed-by: Yuan Liu > Signed-off-by: Tianyou Li > --- > mm/internal.h | 8 ++++- > mm/memory_hotplug.c | 79 ++++++++++++++++++++++++++++++++++++++++++--- > mm/mm_init.c | 36 +++++++++++++-------- > 3 files changed, 103 insertions(+), 20 deletions(-) > > diff --git a/mm/internal.h b/mm/internal.h > index 1561fc2ff5b8..a94928520a55 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -730,7 +730,13 @@ static inline struct page *pageblock_pfn_to_page(unsigned long start_pfn, > return __pageblock_pfn_to_page(start_pfn, end_pfn, zone); > } > > -void set_zone_contiguous(struct zone *zone); > +enum zone_contiguous_state { > + CONTIGUOUS_DEFINITELY_NOT = 0, > + CONTIGUOUS_DEFINITELY = 1, > + CONTIGUOUS_UNDETERMINED = 2, No need for the values. > +}; I don't like that the defines don't match the enum name (zone_c... vs. CONT... ). Essentially you want a "yes / no / maybe" tristate. I don't think we have an existing type for that, unfortunately. enum zone_contig_state { ZONE_CONTIG_YES, ZONE_CONTIG_NO, ZONE_CONTIG_MAYBE, }; Maybe someone reading along has a better idea. > + > +void set_zone_contiguous(struct zone *zone, enum zone_contiguous_state state); > bool pfn_range_intersects_zones(int nid, unsigned long start_pfn, > unsigned long nr_pages); > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 0be83039c3b5..b74e558ce822 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -544,6 +544,32 @@ static void update_pgdat_span(struct pglist_data *pgdat) > pgdat->node_spanned_pages = node_end_pfn - node_start_pfn; > } > > +static enum zone_contiguous_state __meminit clear_zone_contiguous_for_shrinking( > + struct zone *zone, unsigned long start_pfn, unsigned long nr_pages) > +{ > + const unsigned long end_pfn = start_pfn + nr_pages; > + enum zone_contiguous_state result = CONTIGUOUS_UNDETERMINED; > + > + /* > + * If the removed pfn range inside the original zone span, the contiguous > + * property is surely false. > + */ > + if (start_pfn > zone->zone_start_pfn && end_pfn < zone_end_pfn(zone)) > + result = CONTIGUOUS_DEFINITELY_NOT; > + > + /* > + * If the removed pfn range is at the beginning or end of the > + * original zone span, the contiguous property is preserved when > + * the original zone is contiguous. > + */ > + else if (start_pfn == zone->zone_start_pfn || end_pfn == zone_end_pfn(zone)) > + result = zone->contiguous ? > + CONTIGUOUS_DEFINITELY : CONTIGUOUS_UNDETERMINED; > + See my comment below on how to make this readable. > + clear_zone_contiguous(zone); > + return result; > +} > + > void remove_pfn_range_from_zone(struct zone *zone, > unsigned long start_pfn, > unsigned long nr_pages) > @@ -551,6 +577,7 @@ void remove_pfn_range_from_zone(struct zone *zone, > const unsigned long end_pfn = start_pfn + nr_pages; > struct pglist_data *pgdat = zone->zone_pgdat; > unsigned long pfn, cur_nr_pages; > + enum zone_contiguous_state contiguous_state = CONTIGUOUS_UNDETERMINED; > > /* Poison struct pages because they are now uninitialized again. */ > for (pfn = start_pfn; pfn < end_pfn; pfn += cur_nr_pages) { > @@ -571,12 +598,13 @@ void remove_pfn_range_from_zone(struct zone *zone, > if (zone_is_zone_device(zone)) > return; > > - clear_zone_contiguous(zone); > + contiguous_state = clear_zone_contiguous_for_shrinking( > + zone, start_pfn, nr_pages); > Reading this again, I wonder whether it would be nicer to have something like: new_contig_state = zone_contig_state_after_shrinking(); clear_zone_contiguous(zone); or sth like that. Similar for the growing case. > shrink_zone_span(zone, start_pfn, start_pfn + nr_pages); > update_pgdat_span(pgdat); > > - set_zone_contiguous(zone); > + set_zone_contiguous(zone, contiguous_state); > } > > /** > @@ -736,6 +764,47 @@ static inline void section_taint_zone_device(unsigned long pfn) > } > #endif > > +static enum zone_contiguous_state __meminit clear_zone_contiguous_for_growing( > + struct zone *zone, unsigned long start_pfn, unsigned long nr_pages) > +{ > + const unsigned long end_pfn = start_pfn + nr_pages; > + enum zone_contiguous_state result = CONTIGUOUS_UNDETERMINED; > + > + /* > + * Given the moved pfn range's contiguous property is always true, > + * under the conditional of empty zone, the contiguous property should > + * be true. > + */ I don't think that comment is required. > + if (zone_is_empty(zone)) > + result = CONTIGUOUS_DEFINITELY; > + > + /* > + * If the moved pfn range does not intersect with the original zone span, > + * the contiguous property is surely false. > + */ > + else if (end_pfn < zone->zone_start_pfn || start_pfn > zone_end_pfn(zone)) > + result = CONTIGUOUS_DEFINITELY_NOT; > + > + /* > + * If the moved pfn range is adjacent to the original zone span, given > + * the moved pfn range's contiguous property is always true, the zone's > + * contiguous property inherited from the original value. > + */ > + else if (end_pfn == zone->zone_start_pfn || start_pfn == zone_end_pfn(zone)) > + result = zone->contiguous ? > + CONTIGUOUS_DEFINITELY : CONTIGUOUS_DEFINITELY_NOT; > + > + /* > + * If the original zone's hole larger than the moved pages in the range, > + * the contiguous property is surely false. > + */ > + else if (nr_pages < (zone->spanned_pages - zone->present_pages)) > + result = CONTIGUOUS_DEFINITELY_NOT; > + This is a bit unreadable :) if (zone_is_empty(zone)) { result = CONTIGUOUS_DEFINITELY; } else if (...) { /* ... */ ... } else if (...) { ... } > + clear_zone_contiguous(zone); > + return result; > +} > + > /* > * Associate the pfn range with the given zone, initializing the memmaps > * and resizing the pgdat/zone data to span the added pages. After this > @@ -752,8 +821,8 @@ void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn, > { > struct pglist_data *pgdat = zone->zone_pgdat; > int nid = pgdat->node_id; > - > - clear_zone_contiguous(zone); > + const enum zone_contiguous_state contiguous_state = > + clear_zone_contiguous_for_growing(zone, start_pfn, nr_pages); > > if (zone_is_empty(zone)) > init_currently_empty_zone(zone, start_pfn, nr_pages); > @@ -783,7 +852,7 @@ void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn, > MEMINIT_HOTPLUG, altmap, migratetype, > isolate_pageblock); > > - set_zone_contiguous(zone); > + set_zone_contiguous(zone, contiguous_state); > } > > struct auto_movable_stats { > diff --git a/mm/mm_init.c b/mm/mm_init.c > index 7712d887b696..06db3fcf7f95 100644 > --- a/mm/mm_init.c > +++ b/mm/mm_init.c > @@ -2263,26 +2263,34 @@ void __init init_cma_pageblock(struct page *page) > } > #endif > > -void set_zone_contiguous(struct zone *zone) > +void set_zone_contiguous(struct zone *zone, enum zone_contiguous_state state) > { > unsigned long block_start_pfn = zone->zone_start_pfn; > unsigned long block_end_pfn; > > - block_end_pfn = pageblock_end_pfn(block_start_pfn); > - for (; block_start_pfn < zone_end_pfn(zone); > - block_start_pfn = block_end_pfn, > - block_end_pfn += pageblock_nr_pages) { > + if (state == CONTIGUOUS_DEFINITELY) { > + zone->contiguous = true; > + return; > + } else if (state == CONTIGUOUS_DEFINITELY_NOT) { > + // zone contiguous has already cleared as false, just return. > + return; > + } else if (state == CONTIGUOUS_UNDETERMINED) { > + block_end_pfn = pageblock_end_pfn(block_start_pfn); > + for (; block_start_pfn < zone_end_pfn(zone); > + block_start_pfn = block_end_pfn, > + block_end_pfn += pageblock_nr_pages) { > > - block_end_pfn = min(block_end_pfn, zone_end_pfn(zone)); > + block_end_pfn = min(block_end_pfn, zone_end_pfn(zone)); > > - if (!__pageblock_pfn_to_page(block_start_pfn, > - block_end_pfn, zone)) > - return; > - cond_resched(); > - } > + if (!__pageblock_pfn_to_page(block_start_pfn, > + block_end_pfn, zone)) > + return; > + cond_resched(); > + } > > - /* We confirm that there is no hole */ > - zone->contiguous = true; > + /* We confirm that there is no hole */ > + zone->contiguous = true; > + } > } > switch (state) { case CONTIGUOUS_DEFINITELY: zone->contiguous = true; return; case CONTIGUOUS_DEFINITELY_NOT: return; default: break; } ... unchanged logic. > /* > @@ -2348,7 +2356,7 @@ void __init page_alloc_init_late(void) > shuffle_free_memory(NODE_DATA(nid)); > > for_each_populated_zone(zone) > - set_zone_contiguous(zone); > + set_zone_contiguous(zone, CONTIGUOUS_UNDETERMINED); > > /* Initialize page ext after all struct pages are initialized. */ > if (deferred_struct_pages) -- Cheers David