On Wed, Apr 12, 2023 at 10:38:04AM +0200, David Hildenbrand wrote: > 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. > I apologize for the confusion, this is my fault. I had assumed that since dax regions can't be pinned, subsequent nodes backed by a dax device could not be pinned. In testing this, this is not the case. Re: long-term pinning, can you be more explicit as to what is considered long-term? Minutes? hours? days? etc If a migration operation is considered short term, then pinning VM memory during migration deals with this issue cleanly. So walking back my statement - give my testing, i don't believe there's a reason for a new zone. > 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 >
