On Mon, Dec 03, 2018 at 10:33:44AM +0100, Alessandro Selli wrote: > On 03/12/18 at 10:05, Adam Borowski wrote: > > realtime greatly reduces atime writes, but it's still too much. > > I wouldn't say so. Since relatime updates atime only relative to the > present ctime and mtime, it's only changed when one of those two is > changed. That is, updating atime does not require a separate write > operation.
That was the original design -- but alas, it was later changed so the atime is updated at least once a day. > > Case in > > point: it's the likely culprit for wasting the SD card that started this > > thread (on a mostly-read load). > > > if that filesystem was mounted with the relatime option (or with no > option at all, since relatime is the default), then it's very unlikely > it caused any more writes that if it was fully disabled. You still rewrite every inode once per day. > > And, update frequency of 1/day happens to > > match the typical backup schedule, making it ruin snapshots just the same > > as strictatime would. > > Uh? How can atime "ruin snapshots"? Every inode has to be updated. That causes a lot of metadata churn, and even takes significant space. Changing this single number tends to cost far more than a page worth of space -- usual snapshot tools (btrfs, lvm, etc) CoW more than just the inode. Thus, for some common loads we're looking at 5% wasted disk space just for atimes. > > So it's time to kill the nasty thing. > > If only it was any nasty. <troll> Some folks say systemd isn't nasty. </troll> Meow! -- ⢀⣴⠾⠻⢶⣦⠀ ⣾⠁⢠⠒⠀⣿⡁ Ivan was a worldly man: born in St. Petersburg, raised in ⢿⡄⠘⠷⠚⠋⠀ Petrograd, lived most of his life in Leningrad, then returned ⠈⠳⣄⠀⠀⠀⠀ to the city of his birth to die. _______________________________________________ Dng mailing list Dng@lists.dyne.org https://mailinglists.dyne.org/cgi-bin/mailman/listinfo/dng
