Re: ext3, mmap() and mtime (was RE: Redhat 7.3 bugfix)

• To: "Jeff D'Angelo" <dangelo@xxxxxxxxxxx>
• Subject: Re: ext3, mmap() and mtime (was RE: Redhat 7.3 bugfix)
• From: "Arthur A. Person" <person@xxxxxxxxxxxxxxxxxx>
• Date: Fri, 2 Aug 2002 13:24:16 -0400 (EDT)

On Fri, 2 Aug 2002, Jeff D'Angelo wrote:

> However I have noticed another quirk with ext3.  Apparently when you write
> changes to a mmap()'ed file, the mtime (and ctime for that matter) on the
> file is not updated in ext3 as it is with ext2 (and Solaris's journalled
> UFS, btw).  This caused us havok when we had a watchdog script check to
> see if the mtime was updating on ldm.pq before paging us about a potential
> problem.

I don't think mmap should be expected to maintain file characteristics.
The reason you use mmap is to efficiently map virtual memory to disk which
I would hope is done at a physical disk access level rather than through
the file system.  If the file characteristics have to be updated every
time you access memory, that would slow things down tremendously.  The
lack of mtime update in ext3 would sound to me like an improvement.

                                   Art.
>
> --
> Jeff D'Angelo
> ZedX, Inc. Systems Group
>

Arthur A. Person
Research Assistant, System Administrator
Penn State Department of Meteorology
email:  person@xxxxxxxxxxxxxxxxxx, phone:  814-863-1563

• References:
  • ext3, mmap() and mtime (was RE: Redhat 7.3 bugfix)
    • From: Jeff D'Angelo