From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-x242.google.com (mail-qt0-x242.google.com [IPv6:2607:f8b0:400d:c0d::242]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 913982095606A for ; Thu, 15 Mar 2018 13:32:06 -0700 (PDT) Received: by mail-qt0-x242.google.com with SMTP id h4so2920863qtn.13 for ; Thu, 15 Mar 2018 13:38:31 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1520705944-6723-1-git-send-email-jix024@eng.ucsd.edu> <1520705944-6723-4-git-send-email-jix024@eng.ucsd.edu> <20180315045401.GB4860@magnolia> From: Arnd Bergmann Date: Thu, 15 Mar 2018 21:38:29 +0100 Message-ID: Subject: Re: [RFC v2 03/83] Add super.h. List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: Andiry Xu Cc: coughlan@redhat.com, "linux-nvdimm@lists.01.org" , Andiry Xu , "Darrick J. Wong" , Dave Chinner , Linux Kernel Mailing List , miklos@szeredi.hu, Jan Kara , Linux FS Devel , Steven Swanson , swhiteho@redhat.com, Jian Xu List-ID: On Thu, Mar 15, 2018 at 6:51 PM, Andiry Xu wrote: > On Thu, Mar 15, 2018 at 2:05 AM, Arnd Bergmann wrote: >> On Thu, Mar 15, 2018 at 7:11 AM, Andiry Xu wrote: > > Superblock mtime is not a big problem as it is updated rarely. 64-bit > seconds and 32-bit nanoseconds make the inode and log entry bigger, > and updating file->atime cannot be done with a single 64bit update. > That may be annoying and needs to use journaling. If this is a big concern, you could use a format similar to what ext4 has: 30 bits of nanoseconds, and 34 bits of seconds, where the upper two bits count the epoch. That gives you a time range from years 1902 to 2446. You could also have a resolution of less than a nanosecond. Note that today, the file time stamps generated by the kernel are in jiffies resolution, so at best one millisecond. However, most modern file systems go with the 64+32 bit timestamps because it's not all that expensive. Arnd _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm