linux-kernel - Re: [RFC PATCH 1/7] x86, mm: ZONE

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Message-ID: <CAPcyv4gEPum_qq7PH0oNx3ntiWTP_1fp4EU+CAj8tm1Oeg-E9w@mail.gmail.com>
Date:	Fri, 14 Aug 2015 15:33:13 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Jerome Glisse <j.glisse@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Boaz Harrosh <boaz@...xistor.com>,
	Rik van Riel <riel@...hat.com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	david <david@...morbit.com>, Ingo Molnar <mingo@...nel.org>,
	Linux MM <linux-mm@...ck.org>, Ingo Molnar <mingo@...hat.com>,
	Mel Gorman <mgorman@...e.de>, "H. Peter Anvin" <hpa@...or.com>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>
Subject: Re: [RFC PATCH 1/7] x86, mm: ZONE_DEVICE for "device memory"

On Fri, Aug 14, 2015 at 3:06 PM, Jerome Glisse <j.glisse@...il.com> wrote:
> On Fri, Aug 14, 2015 at 02:52:15PM -0700, Dan Williams wrote:
>> On Fri, Aug 14, 2015 at 2:37 PM, Jerome Glisse <j.glisse@...il.com> wrote:
>> > On Wed, Aug 12, 2015 at 11:50:05PM -0400, Dan Williams wrote:
[..]
>> > What is the rational for not updating max_pfn, max_low_pfn, ... ?
>> >
>>
>> The idea is that this memory is not meant to be available to the page
>> allocator and should not count as new memory capacity.  We're only
>> hotplugging it to get struct page coverage.
>
> But this sounds bogus to me to rely on max_pfn to stay smaller than
> first_dev_pfn.  For instance you might plug a device that register
> dev memory and then some regular memory might be hotplug, effectively
> updating max_pfn to a value bigger than first_dev_pfn.
>

True.

> Also i do not think that the buddy allocator use max_pfn or max_low_pfn
> to consider page/zone for allocation or not.

Yes, I took it out with no effects.  I'll investigate further whether
we should be touching those variables or not for this new usage.
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