linux-kernel - Re: [PATCH v8 3/3] mm/memory hotplug/unplug: Optimize zone->contiguous update when changes pfn range

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Message-ID: <aXhk2F3gSXHnCo5s@kernel.org>
Date: Tue, 27 Jan 2026 09:10:16 +0200
From: Mike Rapoport <rppt@...nel.org>
To: "Li, Tianyou" <tianyou.li@...el.com>
Cc: David Hildenbrand <david@...nel.org>,
	Oscar Salvador <osalvador@...e.de>,
	Wei Yang <richard.weiyang@...il.com>,
	Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
	Yong Hu <yong.hu@...el.com>, Nanhai Zou <nanhai.zou@...el.com>,
	Yuan Liu <yuan1.liu@...el.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Qiuxu Zhuo <qiuxu.zhuo@...el.com>, Yu C Chen <yu.c.chen@...el.com>,
	Pan Deng <pan.deng@...el.com>, Chen Zhang <zhangchen.kidd@...com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 3/3] mm/memory hotplug/unplug: Optimize
 zone->contiguous update when changes pfn range

Hi,

On Sat, Jan 24, 2026 at 08:43:51PM +0800, Li, Tianyou wrote:
> On 1/22/2026 7:43 PM, Mike Rapoport wrote:
>
> > > +int online_memory_block_pages(unsigned long start_pfn, unsigned long nr_pages,
> > > +			unsigned long nr_vmemmap_pages, struct zone *zone,
> > > +			struct memory_group *group)
> > >   {
> > > +	const bool contiguous = zone->contiguous;
> > > +	enum zone_contig_state new_contiguous_state;
> > >   	int ret;
> > > +	/*
> > > +	 * Calculate the new zone contig state before move_pfn_range_to_zone()
> > > +	 * sets the zone temporarily to non-contiguous.
> > > +	 */
> > > +	new_contiguous_state = zone_contig_state_after_growing(zone, start_pfn,
> > > +							       nr_pages);
> > > +
> > >   	if (nr_vmemmap_pages) {
> > >   		ret = mhp_init_memmap_on_memory(start_pfn, nr_vmemmap_pages, zone);
> > >   		if (ret)
> > > -			return ret;
> > > +			goto restore_zone_contig;
> > But zone_contig_state_after_growing() does not change zone->contiguous. Why
> > do we need to save and restore it?
> 
> Move_pfn_range_to_zone() will clear the zone contiguous state and it was
> invoked by online_pages(). If error occurs after
> move_pfn_range_to_zone() called like in online_pages(), I think we'd better
> to restore the original value if previous zone contiguous state is true.
 
But after move_pfn_range_to_zone() the added pages are still offline, so I
think the zone remains contiguous and the call to
clear_zone_contiguous(zone) should not be there.

BTW, as we have set_zone_contiguous(ZONE_CONTIG_NO) I think we can use it
instead if clear_zone_contiguous() and remove the latter.
 

-- 
Sincerely yours,
Mike.