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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1spmkU-00000000ktC-1OaC; Sun, 15 Sep 2024 10:44:58 +0000 Date: Sun, 15 Sep 2024 11:44:58 +0100 From: Matthew Wilcox To: Christophe Leroy Cc: Mina Almasry , netdev@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Simon Horman , Stephen Rothwell , Jakub Kicinski , David Miller , Paolo Abeni , Linux Next Mailing List , Arnd Bergmann , "linuxppc-dev@lists.ozlabs.org" Subject: Re: [PATCH net-next v1] mm: fix build on powerpc with GCC 14 Message-ID: References: <20240913192036.3289003-1-almasrymina@google.com> <30e8dee7-e98e-42cb-aab3-6b75f1a6316d@csgroup.eu> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <30e8dee7-e98e-42cb-aab3-6b75f1a6316d@csgroup.eu> X-Rspam-User: X-Stat-Signature: cktdgm78uarw3yrgkjzcb6rptzmu7bpy X-Rspamd-Queue-Id: CF3BBA0012 X-Rspamd-Server: rspam02 X-HE-Tag: 1726397101-683210 X-HE-Meta: U2FsdGVkX1/kz3jemToIvrPDX3es/m9509SINs1JJr4FBiTkxKrXk9iVI75OPSmJpNESFRrtv+gdHu/lwF+85tKJzLreQWQLqa0t3Iq6qe9ypAgD9nkFBEgIjvTS685+pqU3Gm6TJcB1MuLTE5QS5TDhlxURTPQ/zcsLo+sIqNXNO+I/M+AR7mbm/NO+VWrTB1aqo+DOgprxkC3JyU+hGjzadJ/hDJjhQA3U8H9PriElO5gmw1OtLNrh3MysfLjW5534X0BwPx8/01M0reNp7hUSZ7dFJJBak7epb0LAiqHLi+CQS86UG6Hm7mhhEMr9xSlMxDmwvCl5lR4zJmtHtLXIMAakllngE4SprYJy4HJ++9Djl3g3sn7BOlm2xH8BsQjKbr4jTXTxtqXuMy/poSYnzcfsVEOV8dvG3BlBWwTwNXZ+tLIsnxY4nc4q/hC94w4uAx+j5CwAp/J9JZZn/eHv9L3O485cvFNeLTHVZ3WxNtwuLxdta189OkAYZnKx0hRPwfBo5qzWwVh/ruHWORcnowzguZZIGmYnFtjh1wwo8RUSGu3eZ+x+CGpKeg6e/JxZWIrQGBkCzLsA1G9M2lZhoSNbXVG2JgEISrC4kEtdzHwi0hXcBkNw1XR4hDeJLD36q+Hf3n2YSVRGqPITMsMzzcHm20Ce9omfw4b9XYF1At7sevB+aQ9vaicWmZQ9H2lm5H6eQ/ijjEwAMHafe2Z15PJdI/J3M3tNX34RQioNptKCOI7mD0GEsXg+BGR4wd0n9mpgPA36t+eqbvgBTSSL2/dBVUv7ec2zcc9SaSFJVvd6Yuf/jCec5t5aIDflkVz5i4MOuY2WgAp8FVfVEfW3ev9+/G+9YVBwPS5rs++DeFLmEOeaoSIde7xb9r6QUVW4MViqqqzhrdAXtneJ5oilAArbJim4zTBySFt+y2b4fPSX9JOmNmiN7OXP7102J9uhEfbxy6gQlA49OrQ EjMzCVcS cgRww17cyxmV5wSIRYu1KuLKU4ZaSkuce5oX3Ek1kgQjXVKLvqPo6gMZ/Vh0gDUuvtwiHfBhc8dpiGOeKa6mih/UCRiWg8K8JOSV2c5glXuYinq6kK5bWO0EoLSJi4OLM6jqg2PJSExLhReu3hM1Ha0dk2A/6srqnJupuhQDmfIqjpsOGF2Z3APP9c0tvsrB3ygTK55RAbELWV/I8GpCIj0eyO0jyMuIaZ2BVDRO93LuA3f+foGTNVRVAGcISrkmTpltcaNjNQ24wHV77/G71KNYaUpeqeJcLw38Id0IpUWud7yY= 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: List-Subscribe: List-Unsubscribe: On Sat, Sep 14, 2024 at 08:50:46AM +0200, Christophe Leroy wrote: > Hi, > > Le 13/09/2024 à 21:22, Matthew Wilcox a écrit : > > On Fri, Sep 13, 2024 at 07:20:36PM +0000, Mina Almasry wrote: > > > +++ b/include/linux/page-flags.h > > > @@ -239,8 +239,8 @@ static inline unsigned long _compound_head(const struct page *page) > > > { > > > unsigned long head = READ_ONCE(page->compound_head); > > > - if (unlikely(head & 1)) > > > - return head - 1; > > > + if (unlikely(head & 1UL)) > > > + return head & ~1UL; > > > return (unsigned long)page_fixed_fake_head(page); > > > > NAK, that pessimises compound_head(). > > > > Can you please give more details on what the difference is ? > > I can't see what it pessimises. In both cases, you test if the value is odd, > when it is odd you make it even. On x86, for example, it is perfectly valid to load a 64-bit value from an offset of 0x2f relative to a pointer. So there's no need to make it even.