On Tue, Aug 21, 2018 at 01:01:00PM -0400, Austin S. Hemmelgarn wrote: > On 2018-08-21 12:05, David Sterba wrote: > > On Tue, Aug 21, 2018 at 10:10:04AM -0400, Austin S. Hemmelgarn wrote: > >> On 2018-08-21 09:32, Janos Toth F. wrote: > >>>>>> so pretty much everyone who wants to avoid the overhead from them can > >>>>>> just > >>>>>> use the `noatime` mount option. > >>> > >>> It would be great if someone finally fixed this old bug then: > >>> https://bugzilla.kernel.org/show_bug.cgi?id=61601 > >>> Until then, it seems practically impossible to use both noatime (this > >>> can't be added as rootflag in the command line and won't apply if the > >>> kernel already mounted the root as RW) and space-cache-v2 (has to be > >>> added as a rootflag along with RW to take effect) for the root > >>> filesystem (at least without an init*fs, which I never use, so can't > >>> tell). > >>> > >> Last I knew, it was fixed. Of course, it's been quite a while since I > >> last tried this, as I run locally patched kernels that have `noatime` as > >> the default instead of `relatime`. > > > > I'm using VMs without initrd, tested the rootflags=noatime and it still > > fails, the same way as in the bugreport. > > > > As the 'noatime' mount option is part of the mount(2) API (passed as a > > bit via mountflags), the remaining option in the filesystem is to > > whitelist the generic options and ignore them. But this brings some > > layering violation question. > > > > On the other hand, this would be come confusing as the user expectation > > is to see the effects of 'noatime'. > > > Ideally there would be a way to get this to actually work properly. I > think ext4 at least doesn't panic, though I'm not sure if it actually > works correctly.
No, ext4 also refuses to mount, the panic happens in VFS that tries either the rootfstype= or all available filesystems. [ 3.763602] EXT4-fs (sda): Unrecognized mount option "noatime" or missing value [ 3.761315] BTRFS info (device sda): unrecognized mount option 'noatime' > Otherwise, the only option for people who want it set is to patch the > kernel to get noatime as the default (instead of relatime). I would > look at pushing such a patch upstream myself actually, if it weren't for > the fact that I'm fairly certain that it would be immediately NACK'ed by > at least Linus, and probably a couple of other people too. An acceptable solution could be to parse the rootflags and translate them to the MNT_* values, ie. what the commandline tool mount does before it calls the mount syscall.
