Date: Fri, 8 May 2015 11:00:44 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Ingo Molnar <mingo@kernel.org>
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
Subject: Re: [PATCH v2 00/10] evacuate struct page from the block layer,
 introduce __pfn_t
Message-ID: <20150508100044.GI889@ZenIV.linux.org.uk>
References: <CAPcyv4hHwW4U8x1_VLGj2Q4a3HxWgK4F4n9qXg8009_n7sxkmg@mail.gmail.com>
 <554BA748.9030804@linux.intel.com>
 <20150507191107.GB22952@gmail.com>
 <20150507193635.GC5966@gmail.com>
 <20150507194832.GB23511@gmail.com>
 <20150507195313.GA23597@gmail.com>
 <20150507201815.GD5966@gmail.com>
 <20150508053759.GA25786@gmail.com>
 <20150508092044.GH889@ZenIV.linux.org.uk>
 <20150508092601.GA11002@gmail.com>
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On Fri, May 08, 2015 at 11:26:01AM +0200, Ingo Molnar wrote:
> 
> * 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!

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