linux-kernel - Re: [PATCH v2 00/10] evacuate struct page from the block layer, introduce __pfn

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Date:	Thu, 7 May 2015 10:42:46 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Boaz Harrosh <boaz@...xistor.com>, Jan Kara <jack@...e.cz>,
	Mike Snitzer <snitzer@...hat.com>, Neil Brown <neilb@...e.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Chris Mason <clm@...com>, Paul Mackerras <paulus@...ba.org>,
	"H. Peter Anvin" <hpa@...or.com>, Christoph Hellwig <hch@....de>,
	Alasdair Kergon <agk@...hat.com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Mel Gorman <mgorman@...e.de>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Jens Axboe <axboe@...nel.dk>, "Theodore Ts'o" <tytso@....edu>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Julia Lawall <Julia.Lawall@...6.fr>, Tejun Heo <tj@...nel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 00/10] evacuate struct page from the block layer,
 introduce __pfn_t

On Thu, May 7, 2015 at 10:36 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Dan Williams <dan.j.williams@...el.com> wrote:
>
>> > Anyway, I did want to say that while I may not be convinced about
>> > the approach, I think the patches themselves don't look horrible.
>> > I actually like your "__pfn_t". So while I (very obviously) have
>> > some doubts about this approach, it may be that the most
>> > convincing argument is just in the code.
>>
>> Ok, I'll keep thinking about this and come back when we have a
>> better story about passing mmap'd persistent memory around in
>> userspace.
>
> So is there anything fundamentally wrong about creating struct page
> backing at mmap() time (and making sure aliased mmaps share struct
> page arrays)?

Something like "get_user_pages() triggers memory hotplug for
persistent memory", so they are actual real struct pages?  Can we do
memory hotplug at that granularity?
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