10:07 a.m.
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(a)soleen.com>
---
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.