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Date:   Thu, 1 Apr 2021 09:28:03 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Christoph Hellwig <hch@infradead.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-cachefs@redhat.com, linux-afs@lists.infradead.org
Subject: Re: [PATCH v6 00/27] Memory Folios
Message-ID: <20210401122803.GB2710221@ziepe.ca>
References: <20210331184728.1188084-1-willy@infradead.org>
 <20210401070537.GB1363493@infradead.org>
 <20210401112656.GA351017@casper.infradead.org>
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On Thu, Apr 01, 2021 at 12:26:56PM +0100, Matthew Wilcox wrote:
> On Thu, Apr 01, 2021 at 08:05:37AM +0100, Christoph Hellwig wrote:
> > On Wed, Mar 31, 2021 at 07:47:01PM +0100, Matthew Wilcox (Oracle) wrote:
> > >  - Mirror members of struct page (for pagecache / anon) into struct folio,
> > >    so (eg) you can use folio->mapping instead of folio->page.mapping
> > 
> > Eww, why?
> 
> So that eventually we can rename page->mapping to page->_mapping and
> prevent the bugs from people doing page->mapping on a tail page.  eg
> https://lore.kernel.org/linux-mm/alpine.LSU.2.11.2103102214170.7159@eggly.anvils/

Is that gcc structure layout randomization stuff going to be a problem
here?

Add some 
  static_assert(offsetof(struct folio,..) == offsetof(struct page,..))

tests to force it?

Jason