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Date:   Tue, 10 Aug 2021 11:13:05 -0700
From:   Dave Hansen <>
To:     "Kirill A. Shutemov" <>,
        Borislav Petkov <>,
        Andy Lutomirski <>,
        Sean Christopherson <>,
        Andrew Morton <>,
        Joerg Roedel <>
Cc:     Andi Kleen <>,
        Kuppuswamy Sathyanarayanan 
        David Rientjes <>,
        Vlastimil Babka <>,
        Tom Lendacky <>,
        Thomas Gleixner <>,
        Peter Zijlstra <>,
        Paolo Bonzini <>,
        Ingo Molnar <>,
        Varad Gautam <>,
        Dario Faggioli <>,,,,,
        "Kirill A. Shutemov" <>
Subject: Re: [PATCH 1/5] mm: Add support for unaccepted memory

> @@ -1001,6 +1004,9 @@ static inline void del_page_from_free_list(struct page *page, struct zone *zone,
>  	if (page_reported(page))
>  		__ClearPageReported(page);
> +	if (PageOffline(page))
> +		clear_page_offline(page, order);
> +
>  	list_del(&page->lru);
>  	__ClearPageBuddy(page);
>  	set_page_private(page, 0);

So, this is right in the fast path of the page allocator.  It's a
one-time thing per 2M page, so it's not permanent.

*But* there's both a global spinlock and a firmware call hidden in
clear_page_offline().  That's *GOT* to hurt if you were, for instance,
running a benchmark while this code path is being tickled.  Not just to

That could be just downright catastrophic for scalability, albeit

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