Messages in this thread | | | Date | Thu, 26 Mar 2009 10:48:43 -0700 | From | Andrew Morton <> | Subject | Re: relatime: update once per day patches (was: ext3 IO latency measurements) |
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On Thu, 26 Mar 2009 18:12:04 +0100 Frans Pop <elendil@planet.nl> wrote:
> On Thursday 26 March 2009, Andrew Morton wrote: > > On Thu, 26 Mar 2009 09:14:28 -0700 (PDT) Linus Torvalds > <torvalds@linux-foundation.org> 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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