On 04/24/2019 02:08 AM, 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. Is there any scenario where less than a 1GB needs to be added on arm64 ? > > 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. devdax (even ZONE_DEVICE) support has not been enabled on arm64 yet. > > 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. devdax has to be 2M aligned ? Does Linux enforce that right now ? > > Allow, better flexibility by making section size configurable. Unless 2M is being enforced from Linux not sure why this is necessary at the moment. > > Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> > --- > arch/arm64/Kconfig | 10 ++++++++++ > arch/arm64/include/asm/sparsemem.h | 2 +- > 2 files changed, 11 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index b5d8cf57e220..a0c5b9d13a7f 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -801,6 +801,16 @@ config ARM64_PA_BITS > default 48 if ARM64_PA_BITS_48 > default 52 if ARM64_PA_BITS_52 > > +config ARM64_SECTION_SIZE_BITS > + int "sparsemem section size shift" > + range 27 30 27 and 28 do not even compile for ARM64_64_PAGES because of MAX_ORDER and SECTION_SIZE mismatch.
