linux-kernel - Re: [PATCH v2] x86/mm: use max memory block size on bare metal

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Message-ID: <20200610171632.uiaucnp65tg6xexk@ca-dmjordan1.us.oracle.com>
Date:   Wed, 10 Jun 2020 13:16:32 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Michal Hocko <mhocko@...nel.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Sistare <steven.sistare@...cle.com>
Subject: Re: [PATCH v2] x86/mm: use max memory block size on bare metal

On Wed, Jun 10, 2020 at 09:30:00AM +0200, David Hildenbrand wrote:
> On 10.06.20 09:20, David Hildenbrand wrote:
> > On 10.06.20 00:54, Daniel Jordan wrote:
> >> @@ -1390,6 +1391,15 @@ static unsigned long probe_memory_block_size(void)
> >>  		goto done;
> >>  	}
> >>  
> >> +	/*
> >> +	 * Use max block size to minimize overhead on bare metal, where
> >> +	 * alignment for memory hotplug isn't a concern.
> >> +	 */
> >> +	if (hypervisor_is_type(X86_HYPER_NATIVE)) {
> >> +		bz = MAX_BLOCK_SIZE;
> >> +		goto done;
> >> +	}
> > 
> > I'd assume that bioses on physical machines >= 64GB will not align
> > bigger (>= 2GB) DIMMs to something < 2GB.
> > 
> > Acked-by: David Hildenbrand <david@...hat.com>

Thanks!

> FTWT, setup_arch() does the init_hypervisor_platform() call. I assume
> that should be early enough.

I checked all the places where x86 uses memory_block_size_bytes(), it looks ok.