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

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Message-ID: <20150508100044.GI889@ZenIV.linux.org.uk>
Date:	Fri, 8 May 2015 11:00:44 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Jerome Glisse <j.glisse@...il.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Dan Williams <dan.j.williams@...el.com>,
	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>,
	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@...1.01.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>,
	paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH v2 00/10] evacuate struct page from the block layer,
 introduce __pfn_t

On Fri, May 08, 2015 at 11:26:01AM +0200, Ingo Molnar wrote:
> 
> * Al Viro <viro@...IV.linux.org.uk> wrote:
> 
> > On Fri, May 08, 2015 at 07:37:59AM +0200, Ingo Molnar wrote:
> > 
> > > So if code does iov_iter_get_pages_alloc() on a user address that 
> > > has a real struct page behind it - and some other code does a 
> > > regular get_user_pages() on it, we'll have two sets of struct page 
> > > descriptors, the 'real' one, and a fake allocated one, right?
> > 
> > Huh?  iov_iter_get_pages() is given an array of pointers to struct 
> > page, which it fills with what it finds.  iov_iter_get_pages_alloc() 
> > *allocates* such an array, fills that with what it finds and gives 
> > the allocated array to caller.
> > 
> > We are not allocating any struct page instances in either of those.
> 
> Ah, stupid me - thanks for the explanation!

	My fault, actually - this "pages array" should've been either
"'pages' array" or "array of pointers to struct page".
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