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djwong@kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, dchinner@redhat.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, tytso@mit.edu, jbongio@google.com, linux-scsi@vger.kernel.org, ming.lei@redhat.com, jaswin@linux.ibm.com, bvanassche@acm.org References: <20231212110844.19698-1-john.g.garry@oracle.com> <20231212110844.19698-5-john.g.garry@oracle.com> <20231213112026.kkfcwtg64kiadhn5@quack3> Content-Language: en-US From: John Garry Organization: Oracle Corporation In-Reply-To: <20231213112026.kkfcwtg64kiadhn5@quack3> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: LO4P123CA0124.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:192::21) To DM6PR10MB4313.namprd10.prod.outlook.com (2603:10b6:5:212::20) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR10MB4313:EE_|DS0PR10MB6799:EE_ 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X-CRM114-Status: GOOD ( 18.83 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On 13/12/2023 11:20, Jan Kara wrote: >> To allow for further expansion, increase from unsigned int to unsigned >> long. >> >> Since the dma-buf driver prints the file->f_mode member, change the print >> as necessary to deal with the larger size. >> >> Signed-off-by: John Garry > Uh, Al has more experience with fmode_t changes so I'd defer final decision > to him but to me this seems dangerous. Ack > Firstly, this breaks packing of > struct file on 64-bit architectures and struct file is highly optimized for > cache efficiency (see the comment before the struct definition). From pahole, I think that we still fit on the same 64B cacheline (x86_64), but some padding has been added. Before: struct file { union { struct llist_node f_llist; /* 0 8 */ struct callback_head f_rcuhead __attribute__((__aligned__(8))); /* 0 16 */ unsigned int f_iocb_flags; /* 0 4 */ } __attribute__((__aligned__(8))); /* 0 16 */ spinlock_t f_lock; /* 16 4 */ fmode_t f_mode; /* 20 4 */ atomic_long_t f_count; /* 24 8 */ struct mutex f_pos_lock; /* 32 32 */ /* --- cacheline 1 boundary (64 bytes) --- */ After: struct file { union { struct llist_node f_llist /* 0 8 */ struct callback_head f_rcuhead __attribute__((__aligned__(8))); /* 0 16 */ unsigned int f_iocb_flags; /* 0 4 */ } __attribute__((__aligned__(8))); /* 0 16 */ spinlock_t f_lock; /* 16 4 */ /* XXX 4 bytes hole, try to pack */ fmode_t f_mode; /* 24 8 */ atomic_long_t f_count; /* 32 8 */ struct mutex f_pos_lock; /* 40 32 */ /* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */ > Secondly > this will probably generate warnings on 32-bit architectures as there > sizeof(unsigned long) == sizeof(unsigned int) and so your new flags won't > fit anyway? Right, it would then need to be unsigned long long. Or add another 32b member for extended modes. There were no i386 build warnings. Thanks, John