On Thu, Apr 25, 2019 at 05:25:50PM +0200, Michal Hocko wrote: > On Tue 23-04-19 16:38:43, Pavel Tatashin wrote: > > sparsemem section size determines the maximum size and alignment that > > is allowed to offline/online memory block. The bigger the size the less > > the clutter in /sys/devices/system/memory/*. On the other hand, however, > > there is less flexability in what granules of memory can be added and > > removed. > > > > Recently, it was enabled in Linux to hotadd persistent memory that > > can be either real NV device, or reserved from regular System RAM > > and has identity of devdax. > > > > The problem is that because ARM64's section size is 1G, and devdax must > > have 2M label section, the first 1G is always missed when device is > > attached, because it is not 1G aligned. > > > > Allow, better flexibility by making section size configurable. > > Is there any inherent reason (64k page size?) that enforces such a large > memsection? I gave *vague* memories of running out of bits in the page flags if we changed this, but that was a while back. If that's no longer the case, then I'm open to changing the value, but I really don't want to expose it as a Kconfig option as proposed in this patch. People won't have a clue what to set and it doesn't help at all with the single-Image effort. Will
