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[142.162.115.133]) by smtp.gmail.com with ESMTPSA id d2sm3218920qte.84.2021.04.01.05.28.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Apr 2021 05:28:04 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1lRwQd-006jmF-Tc; Thu, 01 Apr 2021 09:28:03 -0300 Date: Thu, 1 Apr 2021 09:28:03 -0300 From: Jason Gunthorpe To: Matthew Wilcox Cc: Christoph Hellwig , 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210401112656.GA351017@casper.infradead.org> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: B157C40002C1 X-Stat-Signature: ep8g7gxxi9yjsueiqmai3s4szxxfk8u5 Received-SPF: none (ziepe.ca>: No applicable sender policy available) receiver=imf02; identity=mailfrom; envelope-from=""; helo=mail-qk1-f181.google.com; client-ip=209.85.222.181 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617280083-985453 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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