On Mon, Feb 10, 2025 at 01:00:02AM -0500, Gregory Price wrote: > On Mon, Feb 10, 2025 at 11:33:47AM +0900, Harry (Hyeonggon) Yoo wrote: > > > > Premise: Some ZONE_NORMAL capacity exists on CXL memory > > due to its large capacity. > > > What you actually need to show to justify increasing the complexity is > (at least - but not limited to) > > 1) structures you want to migrate are harmful when placed on slow memory > > ex) Is `struct page` on slow mem actually harmful? - no data? Then we can hold this one until it turns out it's harmful or give up. > ex) Are page tables on slow mem actually harmful? - known, yes. Defenitly yes. What can be the next? > 2) The structures cannot be made to take up less space on local tier > > ex) struct page can be shrunk - do that first > ex) huge-pages can be deployed - do that first I'm really courious about this. Is there any reason that we should work these in a serialized manner? > 3) the structures take up sufficient space that it matters > > ex) struct page after shrunk might not - do that first > ex) page tables with multi-sized huge pages may not - do that first Same. Should it be serialized? > 4) Making the structures migratable actually does something useful > > are `struct page` or page tables after #2 and #3 both: > > a) going through hot/cold phases enough to warrant being tiered > > b) hot enough for long enough that migration matters? > > You can probably actually (maybe?) collect data on this today - but > you still have to contend with #2 and #3. Ah. You seem to mean those works should be serialized. Right? If it should be for some reason, then it could be sensible. Byungchul > > I don't understand why we shouldn't introduce more kernel movable memory > > if that turns out to be beneficial? > > > > No one is going to stop research you want to do. I'm simply expressing > that I think it's an ill-advised path to take. > > ~Gregory
