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Subject: Re: [PATCH 1/5] mm: Add support for unaccepted memory
To: Dave Hansen <dave.hansen@intel.com>,
 "Kirill A. Shutemov" <kirill@shutemov.name>, Borislav Petkov <bp@alien8.de>,
 Andy Lutomirski <luto@kernel.org>, Sean Christopherson <seanjc@google.com>,
 Andrew Morton <akpm@linux-foundation.org>, Joerg Roedel <jroedel@suse.de>
Cc: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>,
 David Rientjes <rientjes@google.com>, Vlastimil Babka <vbabka@suse.cz>,
 Tom Lendacky <thomas.lendacky@amd.com>, Thomas Gleixner
 <tglx@linutronix.de>, Peter Zijlstra <peterz@infradead.org>,
 Paolo Bonzini <pbonzini@redhat.com>, Ingo Molnar <mingo@redhat.com>,
 Varad Gautam <varad.gautam@suse.com>, Dario Faggioli <dfaggioli@suse.com>,
 x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev,
 linux-kernel@vger.kernel.org,
 "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
References: <20210810062626.1012-1-kirill.shutemov@linux.intel.com>
 <20210810062626.1012-2-kirill.shutemov@linux.intel.com>
 <d091b333-9ef8-ac32-58c5-c325d29f26d7@intel.com>
From: Andi Kleen <ak@linux.intel.com>
Message-ID: <9748c07c-4e59-89d0-f425-c57f778d1b42@linux.intel.com>
Date: Tue, 10 Aug 2021 11:30:55 -0700
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> 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
> temporarily

This would be only a short blib at initialization until the system 
reaches steady state. So yes it would be temporary, but very short at that.

-Andi