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 on disk might be out of date by at most 24 hours.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 memâ
> ory. The on-disk timestamps are updated only when:
> (a) the inode needs to be updated for some change unreâ
> lated to file timestamps;
> (b) the application employs fsync(2), syncfs(2), or
> (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 mtime fields on disk might be out of date by up to 24
> Examples of workloads where this option could be of sigâ
> nificant benefit include frequent random writes to preâ
> allocated files, as well as cases where the MS_STRICTAâ
> 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
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/
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