From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f170.google.com ([209.85.192.170]:41930 "EHLO mail-pd0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752008AbbB0IIC (ORCPT ); Fri, 27 Feb 2015 03:08:02 -0500 Received: by pdno5 with SMTP id o5so19379849pdn.8 for ; Fri, 27 Feb 2015 00:08:01 -0800 (PST) Date: Fri, 27 Feb 2015 00:08:00 -0800 From: Omar Sandoval To: "Michael Kerrisk (man-pages)" Cc: "Theodore Ts'o" , Eric Sandeen , linux-man@vger.kernel.org, Linux API , XFS Developers , Linux-Fsdevel , Ext4 Developers List , Linux btrfs Developers List Subject: Re: Documenting MS_LAZYTIME Message-ID: <20150227080800.GA20442@mew> References: <54E7578E.4090809@redhat.com> <20150221025636.GB7922@thunk.org> <54EEDE23.6080009@gmail.com> <20150226133113.GD11217@thunk.org> <54EF2161.90607@gmail.com> <20150227000409.GC17174@thunk.org> <54F02446.2050008@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: <54F02446.2050008@gmail.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Fri, Feb 27, 2015 at 09:01:10AM +0100, Michael Kerrisk (man-pages) wrote: > On 02/27/2015 01:04 AM, Theodore Ts'o wrote: > > On Thu, Feb 26, 2015 at 02:36:33PM +0100, Michael Kerrisk (man-pages) wrote: > >> > >> The disadvantage of MS_STRICTATIME | MS_LAZYTIME is that > >> in the case of a system crash, the atime and mtime fields > >> on disk might be out of date by at most 24 hours. > > > > I'd change to "The disadvantage of MS_LAZYTIME is that..." and > > perhaps move that so it's clear it applies to any use of MS_LAZYTIME > > has this as a downside. > > > > Does that make sense? > > Thanks, Ted. Got it. So, now we have: > > MS_LAZYTIME (since Linux 3.20) > Reduce on-disk updates of inode timestamps (atime, > mtime, ctime) by maintaining these changes only in mem‐ > ory. The on-disk timestamps are updated only when: > > (a) the inode needs to be updated for some change unre‐ > lated to file timestamps; > > (b) the application employs fsync(2), syncfs(2), or > sync(2); > > (c) an undeleted inode is evicted from memory; or > > (d) more than 24 hours have passed since the inode was > written to disk. > > This mount significantly reduces writes needed to update "This mount option"? > the inode's timestamps, especially mtime and atime. > However, in the event of a system crash, the atime and > mtime fields on disk might be out of date by up to 24 > hours. > > Examples of workloads where this option could be of sig‐ > nificant benefit include frequent random writes to pre‐ > allocated files, as well as cases where the MS_STRICTA‐ > TIME mount option is also enabled. (The advantage of > (MS_STRICTATIME | MS_LAZYTIME) is that stat(2) will > return the correctly updated atime, but the atime > updates will be flushed to disk only when (1) the inode > needs to be updated for filesystem / data consistency > reasons or (2) the inode is pushed out of memory, or (3) > the filesystem is unmounted.) Is it necessary to repeat the reasons for flushing, which are stated above? > > Cheers, > > Michael > > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/ > > _______________________________________________ > xfs mailing list > xfs@oss.sgi.com > http://oss.sgi.com/mailman/listinfo/xfs Thanks! -- Omar