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Howlett" , John Hubbard , Naoya Horiguchi , Hugh Dickins , Suren Baghdasaryan , Alex Sierra , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: extend max struct page size for kmsan Message-ID: References: <20230130130739.563628-1-arnd@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: CC2BC18001B X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: jph5wnxth4hmasc65hfuxrih8o4e8stb X-HE-Tag: 1675097294-623998 X-HE-Meta: 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 NxSZKCUe Q/JGBSuD4LTi1udrV6wcDHhHJLe6NGw8hvMv5dogRAes8kjebTKJUgxaLQQpSbyfUmBGAIzMr2NxRd2lQfWIC4BwlDdGosMwoKs6KcgYtpESqLz0x4/lIm4eSKB2QaDCxlWhFiMFkRf49O+d9EIgatsDNo0XNMpL+f/yMK05S8t7tqq4O6vl4QweAsPs2/0E5DrNDYN8mtNEST541vD+9kTsMyg== 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 Mon, Jan 30, 2023 at 02:38:22PM +0100, Michal Hocko wrote: > On Mon 30-01-23 14:07:26, Arnd Bergmann wrote: > > From: Arnd Bergmann > > > > After x86 has enabled support for KMSAN, it has become possible > > to have larger 'struct page' than was expected when commit > > 5470dea49f53 ("mm: use mm_zero_struct_page from SPARC on all 64b > > architectures") was merged: > > > > include/linux/mm.h:156:10: warning: no case matching constant switch condition '96' > > switch (sizeof(struct page)) { > > > > Extend the maximum accordingly. > > > > Fixes: 5470dea49f53 ("mm: use mm_zero_struct_page from SPARC on all 64b architectures") > > Fixes: 4ca8cc8d1bbe ("x86: kmsan: enable KMSAN builds for x86") > > Signed-off-by: Arnd Bergmann > > Acked-by: Michal Hocko > > I haven't really followed KMSAN development but I would have expected > that it would, like other debugging tools, add its metadata to page_ext > rather than page directly. Yes, that would have been preferable. Also, I don't understand why we need an entire page to store whether each "bit" of a page is initialised. There are no CPUs which have bit-granularity stores; either you initialise an entire byte or not. So that metadata can shrink from 4096 bytes to 512.