On 12.04.23 04:54, Huang, Ying wrote:
Gregory Price <gregory.price@xxxxxxxxxxxx> writes:
On Tue, Apr 11, 2023 at 02:37:50PM +0800, Huang, Ying wrote:
Gregory Price <gregory.price@xxxxxxxxxxxx> writes:
[snip]
2. During the migration process, the memory needs to be forced not to be
migrated to another node by other means (tiering software, swap,
etc). The obvious way of doing this would be to migrate and
temporarily pin the page... but going back to problem #1 we see that
ZONE_MOVABLE and Pinning are mutually exclusive. So that's
troublesome.
Can we use memory policy (cpusets, mbind(), set_mempolicy(), etc.) to
avoid move pages out of CXL.mem node? Now, there are gaps in tiering,
but I think it is fixable.
Best Regards,
Huang, Ying
[snip]
That feels like a hack/bodge rather than a proper solution to me.
Maybe this is an affirmative argument for the creation of an EXMEM
zone.
Let's start with requirements. What is the requirements for a new zone
type?
I'm stills scratching my head regarding this. I keep hearing all
different kind of statements that just add more confusions "we want it
to be hotunpluggable" "we want to allow for long-term pinning memory"
"but we still want it to be movable" "we want to place some unmovable
allocations on it". Huh?
Just to clarify: ZONE_MOVABLE allows for pinning. It just doesn't allow
for long-term pinning of memory.
For good reason, because long-term pinning of memory is just the worst
(memory waste, fragmentation, overcommit) and instead of finding new
ways to *avoid* long-term pinnings, we're coming up with advanced
concepts to work-around the fundamental property of long-term pinnings.
We want all memory to be long-term pinnable and we want all memory to be
movable/hotunpluggable. That's not going to work.
If you'd ask me today, my prediction is that ZONE_EXMEM is not going to
happen.
--
Thanks,
David / dhildenb
