On Mon, Jan 27, 2020 at 6:21 PM Luigi Semenzato <semenzato@xxxxxxxxxx> wrote: > > On Mon, Jan 27, 2020 at 8:28 AM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: > > > > On Mon, Jan 27, 2020 at 5:13 PM Luigi Semenzato <semenzato@xxxxxxxxxx> wrote: > > > > > > On Mon, Jan 27, 2020 at 6:16 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > > > On Fri 24-01-20 08:37:12, Luigi Semenzato wrote: > > > > [...] > > > > > The purpose of my documentation patch was to make it clearer that > > > > > hibernation may fail in situations in which suspend-to-RAM works; for > > > > > instance, when there is no swap, and anonymous pages are over 50% of > > > > > total RAM. I will send a new version of the patch which hopefully > > > > > makes this clearer. > > > > > > > > I was under impression that s2disk is pretty much impossible without any > > > > swap. > > > > > > I am not sure what you mean by "swap" here. S2disk needs a swap > > > partition for storing the image, but that partition is not used for > > > regular swap. > > > > That's not correct. > > > > The swap partition (or file) used by s2disk needs to be made active > > before it can use it and the mm subsystem is also able to use it for > > regular swap then. > > OK---I had this wrong, thanks. > > > > If there is no swap, but more than 50% of RAM is free > > > or reclaimable, s2disk works fine. If anonymous is more than 50%, > > > hibernation can still work, but swap needs to be set up (in addition > > > to the space for the hibernation image). The setup is not obvious and > > > I don't think that the documentation is clear on this. > > > > Well, the entire contents of RAM must be preserved, this way or > > another, during hibernation. That should be totally obvious to anyone > > using it really. > > Yes, that's obvious. > > > Some of the RAM contents is copies of data already there in the > > filesystems on persistent storage and that does not need to be saved > > again. Everything else must be saved and s2disk (and Linux > > hibernation in general) uses active swap space to save these things. > > This implies that in order to hibernate the system, you generally need > > the amount of swap space equal to the size of RAM minus the size of > > files mapped into memory. > > > > So, to be on the safe side, the total amount of swap space to be used > > for hibernation needs to match the size of RAM (even though > > realistically it may be smaller than that in the majority of cases). > > This all makes sense, but we do this: > > -- add resume=/dev/sdc to the command line > -- attach a disk (/dev/sdc) with size equal to RAM > -- mkswap /dev/sdc > -- swapon /dev/sdc > -- echo disk > /sys/power/state > > and the last operation fails with ENOMEM. Are we doing something > wrong? Are we hitting some other mm bug? I would expect this to work, so the fact that it doesn't work for you indicates a bug somewhere or at least an assumption that doesn't hold. Can you please remind me what you do to trigger the unexpected behavior?
