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

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Message-ID: <CA+8MBbL4nqTxi14Lz92PRFZeobHBLimSfcTH=9HaZBcEUpLVOg@mail.gmail.com>
Date:	Fri, 21 Aug 2015 16:54:12 -0700
From:	Tony Luck <tony.luck@...il.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Daniel J Blueman <daniel@...ascale.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Steffen Persvold <sp@...ascale.com>
Subject: Re: [PATCH v4 4/4] Use 2GB memory block size on large-memory x86-64 systems

On Fri, Aug 21, 2015 at 1:50 PM, Yinghai Lu <yinghai@...nel.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
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