Re: [PATCH v4 4/4] Use 2GB memory block size on large-memory x86-64 systems

From: Tony Luck <tony.luck@gmail.com>
To: Yinghai Lu <yinghai@kernel.org>
Cc: Daniel J Blueman <daniel@numascale.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	Steffen Persvold <sp@numascale.com>
Subject: Re: [PATCH v4 4/4] Use 2GB memory block size on large-memory x86-64 systems
Date: Fri, 21 Aug 2015 16:54:12 -0700	[thread overview]
Message-ID: <CA+8MBbL4nqTxi14Lz92PRFZeobHBLimSfcTH=9HaZBcEUpLVOg@mail.gmail.com> (raw)
In-Reply-To: <CAE9FiQU-=oAzi_benuEm=x_Y_LUp48uND6cGnx9osbYyPWySdw@mail.gmail.com>

On Fri, Aug 21, 2015 at 1:50 PM, Yinghai Lu <yinghai@kernel.org> wrote:
>> It seems that many systems with large amounts of memory
>> will have a nicely aligned max_pfn ... so they will get
>> the 2GB block size.  If they don't have a well aligned
>> max_pfn, then they need to use a smaller size to avoid
>> the crash I saw.
>
> Good to me.

Still stuff going on that I don't understand here. I increased the amount of
mirrored memory in this machine which moved max_pfn to 0x7560000
and probe_memory_block_size() picked 512MB as the memory_block_size,
which seemed plausible.

But my kernel still crashed during boot with this value. :-(
Forcing the block size to 128M made the system boot.

Maybe all the holes in the e820 map matter too (specifically the
alignment of the holes)?

-Tony