From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 83A9617BA1; Mon, 1 Jul 2024 22:49:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719874182; cv=none; b=u8aARWDsdSmta65FJP7jdRsONCSILIPbhNjoNxNDjna5/8HN2sbvjeLrz+82mZwHRyKdxvJCY0ZSkJllQcPkN4FStsa0Y5nq1Yu7+gMlraODZoSmdYt5s+I6PuSVtZYpiYq5XAwy8UcfrUyNgn5oVQiFx/fLhWqSo2SXbgTaAzw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719874182; c=relaxed/simple; bh=bXoWDyduCGsJU7lhbujiLjxLA54PjQmw5SMTkVT0vNc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=aOY/q+lHQEjFSLMAP6FTF6ABlk/W+rHq8cstR2cufqvdkpcyY/bheoWssnzP60UyzgRJFBPw+qorbB2GSZA7fj6Owf8L3dXNhiZXduxAxULjxBJE+RmmlYTs6vFRRCuWxNb9QS4L33p2fJGXz9Lqt92y46LzwYMpI9EXaClcxm0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MnsIb0uN; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MnsIb0uN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 02F84C116B1; Mon, 1 Jul 2024 22:49:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1719874182; bh=bXoWDyduCGsJU7lhbujiLjxLA54PjQmw5SMTkVT0vNc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MnsIb0uNSwAHfqytxz2YxarQKag9GysdcNIBeUK8dH1tzYMDJUfwlKcSo9NyetHFj 4gRTea8CYRA/mwIDw8oQW65xy5aeE/FMx8dHovVUqnwGBQ4AMIi7TwrfpiY//28W68 GrtBUsMP/EL1H25z91QNWBL63F7TRQUhp19y5VK0+7ldauGeatdJextRuf2x+nFj+D iToBZrGCa+a2CZZd1KHEMQIfFgam7OVr+YJ9P0s1scV4VsWOy36sQp+RFpToV/BKr+ x2PWAcV1CMKmDKqSRrQjQTblzn4M2tyZE92FrpeA94E7MCwdHtrYNE606nDiRjp05o 7pAp5zCFIgkUg== Date: Mon, 1 Jul 2024 15:49:41 -0700 From: "Darrick J. 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> Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240626-mgtime-v1-1-a189352d0f8f@kernel.org> 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 > >