linux-kernel - Re: [PATCH v8 4/8] mm,memory_hotplug: Allocate memmap from the added memory range

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Message-ID: <b0f5f87c-af03-173c-17e3-ccf15ccb9cb1@redhat.com>
Date:   Fri, 16 Apr 2021 13:07:06 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 4/8] mm,memory_hotplug: Allocate memmap from the added
 memory range


> -int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
> -		       int online_type, int nid)
> +int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages,
> +			      struct zone *zone)
> +{
> +	unsigned long end_pfn = pfn + nr_pages;
> +	int ret;
> +
> +	ret = kasan_add_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages));
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * Initialize vmemmap pages with the corresponding node, zone links set.

The "set" sounds weird. I'd remove that comment completely.

> +	 */
> +	move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE);
> +
> +	/*
> +	 * It might be that the vmemmap_pages fully span sections. If that is
> +	 * the case, mark those sections online here as otherwise they will be
> +	 * left offline.
> +	 */
> +	if (nr_pages >= PAGES_PER_SECTION)
> +	        online_mem_sections(pfn, ALIGN_DOWN(end_pfn, PAGES_PER_SECTION));
> +
> +	return ret;
> +}
> +
> +void mhp_deinit_memmap_on_memory(unsigned long pfn, unsigned long nr_pages)
> +{
> +	unsigned long end_pfn = pfn + nr_pages;
> +        /*
> +	 * The pages associated with this vmemmap have been offlined, so
> +	 * we can reset its state here.
> +	 */
> +	remove_pfn_range_from_zone(page_zone(pfn_to_page(pfn)), pfn, nr_pages);
> +	kasan_remove_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages));
> +
> +	/*
> +	 * It might be that the vmemmap_pages fully span sections. If that is
> +	 * the case, mark those sections offline here as otherwise they will be
> +	 * left online.
> +	 */
> +	if (nr_pages >= PAGES_PER_SECTION)
> +		offline_mem_sections(pfn, ALIGN_DOWN(end_pfn, PAGES_PER_SECTION));

It's usually best if you undo stuff in the complete opposite order. For 
example at this point, the memmap might already have been poisoned, yet 
pfn_to_online_page() would return true. You should do that first.

Apart from that, nothing jumped at me :)

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb