On Mon, Jan 6, 2020 at 1:53 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > On Thu 26-12-19 14:02:04, Luigi Semenzato wrote: > [...] > > +Limitations of Hibernation > > +========================== > > + > > +When entering hibernation, the kernel tries to allocate a chunk of memory large > > +enough to contain a copy of all pages in use, to use it for the system > > +snapshot. If the allocation fails, the system cannot hibernate and the > > +operation fails with ENOMEM. This will happen, for instance, when the total > > +amount of anonymous pages (process data) exceeds 1/2 of total RAM. > > + > > +One possible workaround (besides terminating enough processes) is to force > > +excess anonymous pages out to swap before hibernating. This can be achieved > > +with memcgroups, by lowering memory usage limits with ``echo <new limit> > > > +/dev/cgroup/memory/<group>/memory.mem.usage_in_bytes``. However, the latter > > +operation is not guaranteed to succeed. > > I am not familiar with the hibernation process much. But what prevents > those allocations to reclaim memory and push out the anonymous memory to > the swap on demand during the hibernation's allocations? Nothing in particular AFAICS, at least in theory. The approach taken by the hibernation code is rather straightforward: allocate enough memory to store a copy of every page (in RAM) that needs to be saved. These allocations are made one page at a time, so in theory they should not fail as long as there is enough swap space in the system, but I'm probably missing something here.
