linux-kernel - Re: [PATCHv2 6/7] x86/mm: Provide helpers for unaccepted memory

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Date:   Wed, 12 Jan 2022 22:43:58 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Varad Gautam <varad.gautam@...e.com>,
        Dario Faggioli <dfaggioli@...e.com>, x86@...nel.org,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 6/7] x86/mm: Provide helpers for unaccepted memory

On Tue, Jan 11, 2022 at 12:01:56PM -0800, Dave Hansen wrote:
> On 1/11/22 03:33, Kirill A. Shutemov wrote:
> > Core-mm requires few helpers to support unaccepted memory:
> > 
> >   - accept_memory() checks the range of addresses against the bitmap and
> >     accept memory if needed;
> > 
> >   - maybe_set_page_offline() checks the bitmap and marks a page with
> >     PageOffline() if memory acceptance required on the first
> >     allocation of the page.
> > 
> >   - accept_and_clear_page_offline() accepts memory for the page and clears
> >     PageOffline().
> > 
> ...
> > +void accept_memory(phys_addr_t start, phys_addr_t end)
> > +{
> > +	unsigned long flags;
> > +	if (!boot_params.unaccepted_memory)
> > +		return;
> > +
> > +	spin_lock_irqsave(&unaccepted_memory_lock, flags);
> > +	__accept_memory(start, end);
> > +	spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
> > +}
> 
> Not a big deal, but please cc me on all the patches in the series.  This is
> called from the core mm patches which I wasn't cc'd on.
> 
> This also isn't obvious, but this introduces a new, global lock into the
> fast path of the page allocator and holds it for extended periods of time.
> It won't be taken any more once all memory is accepted, but you can sure bet
> that it will be noticeable until that happens.
> 
> *PLEASE* document this.  It needs changelog and probably code comments.

Okay, will do.

-- 
 Kirill A. Shutemov