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Wong" To: Jeff Layton Cc: Alexander Viro , Christian Brauner , Jan Kara , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Chandan Babu R , Theodore Ts'o , Andreas Dilger , Chris Mason , Josef Bacik , David Sterba , Hugh Dickins , Andrew Morton , kernel-team@fb.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-mm@kvack.org, linux-nfs@vger.kernel.org Subject: Re: [PATCH 01/10] fs: turn inode ctime fields into a single ktime_t Message-ID: <20240701224941.GE612460@frogsfrogsfrogs> References: <20240626-mgtime-v1-0-a189352d0f8f@kernel.org> <20240626-mgtime-v1-1-a189352d0f8f@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240626-mgtime-v1-1-a189352d0f8f@kernel.org> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 4A7C2A0013 X-Stat-Signature: 63jk8pubcym8bsjnd4zosm7j7wqmpdga X-Rspam-User: X-HE-Tag: 1719874183-205175 X-HE-Meta: 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 d+MyAuiL QFolfqHfZbzIAZOQW/FLjQwR7XM/bVwbpvoVN9MfPWV5FwAzc8l+/aW5NAp/JbyRc9eegN+mQFp/8LE7zDe2hysDkfx4gYhmroheD5LWciykmUKBRXvCYVPcuwhBNrwpiPYzX4tpcAyE+h8xdm+ZJdbb0wnjnb30IqA++zN/6MHHEuz8rFaE0VZSA9SrTaxn6OhAqGzyomwUpwqhSd4Y538Vgznlje0CCeGTGBFiupCI4Qm6sNw74l6jJZMGBk+fg/pZf9IgjDQb/+UY+GSvWW731N5eL4a60GRs80XwFlXhmLQvTHsgAATpx5882r1qp5hMDN/AnPo2OMRA= 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 Wed, Jun 26, 2024 at 09:00:21PM -0400, Jeff Layton wrote: > The ctime is not settable to arbitrary values. It always comes from the > system clock, so we'll never stamp an inode with a value that can't be > represented there. If we disregard people setting their system clock > past the year 2262, there is no reason we can't replace the ctime fields > with a ktime_t. > > Switch the ctime fields to a single ktime_t. Move the i_generation down > above i_fsnotify_mask and then move the i_version into the resulting 8 > byte hole. This shrinks struct inode by 8 bytes total, and should > improve the cache footprint as the i_version and ctime are usually > updated together. > > The one downside I can see to switching to a ktime_t is that if someone > has a filesystem with files on it that has ctimes outside the ktime_t > range (before ~1678 AD or after ~2262 AD), we won't be able to display > them properly in stat() without some special treatment in the > filesystem. The operating assumption here is that that is not a > practical problem. What happens if a filesystem with the ability to store ctimes beyond whatever ktime_t supports (AFAICT 2^63-1 nanonseconds on either side of the Unix epoch)? I think the behavior with your patch is that ktime_set clamps the ctime on iget because the kernel can't handle it? It's a little surprising that the ctime will suddenly jump back in time to 2262, but maybe you're right that nobody will notice or care? ;) --D > > Signed-off-by: Jeff Layton > --- > include/linux/fs.h | 26 +++++++++++--------------- > 1 file changed, 11 insertions(+), 15 deletions(-) > > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 5ff362277834..5139dec085f2 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -662,11 +662,10 @@ struct inode { > loff_t i_size; > time64_t i_atime_sec; > time64_t i_mtime_sec; > - time64_t i_ctime_sec; > u32 i_atime_nsec; > u32 i_mtime_nsec; > - u32 i_ctime_nsec; > - u32 i_generation; > + ktime_t __i_ctime; > + atomic64_t i_version; > spinlock_t i_lock; /* i_blocks, i_bytes, maybe i_size */ > unsigned short i_bytes; > u8 i_blkbits; > @@ -701,7 +700,6 @@ struct inode { > struct hlist_head i_dentry; > struct rcu_head i_rcu; > }; > - atomic64_t i_version; > atomic64_t i_sequence; /* see futex */ > atomic_t i_count; > atomic_t i_dio_count; > @@ -724,6 +722,8 @@ struct inode { > }; > > > + u32 i_generation; > + > #ifdef CONFIG_FSNOTIFY > __u32 i_fsnotify_mask; /* all events this inode cares about */ > /* 32-bit hole reserved for expanding i_fsnotify_mask */ > @@ -1608,29 +1608,25 @@ static inline struct timespec64 inode_set_mtime(struct inode *inode, > return inode_set_mtime_to_ts(inode, ts); > } > > -static inline time64_t inode_get_ctime_sec(const struct inode *inode) > +static inline struct timespec64 inode_get_ctime(const struct inode *inode) > { > - return inode->i_ctime_sec; > + return ktime_to_timespec64(inode->__i_ctime); > } > > -static inline long inode_get_ctime_nsec(const struct inode *inode) > +static inline time64_t inode_get_ctime_sec(const struct inode *inode) > { > - return inode->i_ctime_nsec; > + return inode_get_ctime(inode).tv_sec; > } > > -static inline struct timespec64 inode_get_ctime(const struct inode *inode) > +static inline long inode_get_ctime_nsec(const struct inode *inode) > { > - struct timespec64 ts = { .tv_sec = inode_get_ctime_sec(inode), > - .tv_nsec = inode_get_ctime_nsec(inode) }; > - > - return ts; > + return inode_get_ctime(inode).tv_nsec; > } > > static inline struct timespec64 inode_set_ctime_to_ts(struct inode *inode, > struct timespec64 ts) > { > - inode->i_ctime_sec = ts.tv_sec; > - inode->i_ctime_nsec = ts.tv_nsec; > + inode->__i_ctime = ktime_set(ts.tv_sec, ts.tv_nsec); > return ts; > } > > > -- > 2.45.2 > >