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Date: Fri, 8 May 2015 11:26:01 +0200
From: Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH v2 00/10] evacuate struct page from the block layer,
 introduce __pfn_t
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To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Jerome Glisse <j.glisse@gmail.com>, Dave Hansen <dave.hansen@linux.intel.com>, Dan Williams <dan.j.williams@intel.com>, Linus Torvalds <torvalds@linux-foundation.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Boaz Harrosh <boaz@plexistor.com>, Jan Kara <jack@suse.cz>, Mike Snitzer <snitzer@redhat.com>, Neil Brown <neilb@suse.de>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Heiko Carstens <heiko.carstens@de.ibm.com>, Chris Mason <clm@fb.com>, Paul Mackerras <paulus@samba.org>, "H. Peter Anvin" <hpa@zytor.com>, Christoph Hellwig <hch@lst.de>, Alasdair Kergon <agk@redhat.com>, "linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>, Mel Gorman <mgorman@suse.de>, Matthew Wilcox <willy@linux.intel.com>, Ross Zwisler <ross.zwisler@linux.intel.com>, Rik van Riel <riel@redhat.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Jens Axboe <axboe@kernel.dk>, Theodore Ts'o <tytso@mit.edu>, "Martin K. Petersen" <martin.petersen@oracle.com>, Julia Lawall <Julia.Lawall@lip6.fr>, Tejun Heo <tj@kernel.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, paulmck@linux.vnet.ibm.com
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* Al Viro <viro@ZenIV.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!

	Ingo