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    SubjectRe: relatime: update once per day patches (was: ext3 IO latency measurements)
    On Thu, 26 Mar 2009 18:12:04 +0100 Frans Pop <> wrote:

    > On Thursday 26 March 2009, Andrew Morton wrote:
    > > On Thu, 26 Mar 2009 09:14:28 -0700 (PDT) Linus Torvalds
    > <> wrote:
    > > > I generally agree witht he "leave policy to user space" people, but
    > > > this is an area where (a) user space has shown itself to not get it
    > > > right (ie people don't do even the existing relatime because distros
    > > > don't) and (b) what's the alternative?
    > > >
    > > > > I (and others) pointed out that it would be better to implement
    > > > > this as a mount option. That suggestion was met with varying
    > > > > sillinesses and that is where things stand.
    > > >
    > > > I'd suggest first just doing the 24 hour thing, and then, IF user
    > > > space actually ever gets its act together, and people care, and they
    > > > _ask_ for a mount option, that's when it's worth doing.
    > >
    > > We wouldn't normally just enable the new feature by default because it
    > > changes kernel behaviour. Userspace needs to be changed in some manner
    > > to opt-in. One way it's `mount -o remount', the other way it's a poke
    > > in /proc.
    > What change are you talking about here exactly? The "change relatime to
    > have a 24 hour safeguard" of Matthes's first patch or the "enable
    > relatime by default" options in the second patch?
    > For the first I don't think it's that big a deal as it is a change that
    > makes the behavior of relatime safer and not riskier. Also, it's
    > something people have argued should have been part of the initial
    > functionality of relatime (it was part of the discussion back then), and
    > finally for a lot of users it's already current functionality as major
    > distros already do include the patch.
    > For the second, I can see your point and can understand reservations to
    > make enabling relatime a kernel config option.
    > Speaking exclusively for myself, I would be happy enough if only the first
    > of Matthew's patches would get accepted.

    Oh, the feature itself is desirable. But the interface isn't.

    - It's a magic number. Maybe someone runs tmpwatch twice per day, or
    weekly, or...

    - That's fixable by making "24" tunable, but it's still a global
    thing. Better to make it per-fs.

    - mount(8) is the standard way of tuning fs behaviour. There's no
    need to deviate from that here.

    Note that none of this involves the default setting. With a per-mount
    tunable we can still make the default for each fs be "on, 24 hours"
    if we so decide.

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