Remounting a file system with noatime under 2.0.3x

Philip Gladstone (philip@raptor.com)
Tue, 08 Sep 1998 10:12:00 -0400

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Hi,
It turns out that if you remount the root file system
with the noatime option, then things do not work the way that
you (I in particular) would expect.

Specifically, it appears that any file whose inode was cached
*before* the remount will continue to have their atime recorded.
[The mapping of the system mount flags onto the memory inode
is only done when the inode is read from disk.]

It is unclear what the general solution is:

1) When the remount happens, all inodes that refer to that
disk should have their flags changed. [This doesn't work
because in the NOATIME->ATIME case, bacause you can't tell
*why* the NOATIME flag was set.]

2) When the remount happens, flush all the inodes to ensure
that they are reread. [This doesn't work for files which
are open during the remount.]

3) Don't permit the noatime flag to be changed on a remount.
[This means that you can't make the root file system
noatime (which is what I am trying to do)].

4) Some combination of 1 and 2 that gets it right most
of the time.

While I can probably fix it for noatime, it is unclear what the
analogous problems are for the other filesystem flags.

Thoughts

Philip

-- 
Philip Gladstone                           +1 781 530 2461
Raptor Systems / Axent Technologies 
Waltham, MA         		    http://www.raptor.com/
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