On Fri, Feb 07, 2025 at 04:54:10AM -0500, Gregory Price wrote: > On Fri, Feb 07, 2025 at 06:34:43PM +0900, Honggyu Kim wrote: > > On 2/7/2025 5:57 PM, Gregory Price wrote: > > > > > The default kernel stack size is like 16kb. You'd need like 100,000 > > > threads to eat up 1.5GB, and 2048 threads only eats like 32MB. > > > > > > It's not an interesting amount of memory if you have a 20TB system. > > > > The amount might be small, but having those data in slow tier can > > make performance degradation if it is heavily accessed. > > > > The number of accesses isn't linearly corelated to the size of the > > memory region. > > > > Right, I started by saying: > > [CXL is] "generally not fit for kernel use" > > I have the opinion that CXL memory should be defaulted to ZONE_MOVABLE, > but I understand the pressure on ZONE_NORMAL means this may not be > possible for large capacities. Just to clarify, for moderate capacities where ZONE_NORMAL in DRAM covers the whole memory, it's not a big issue since the easiest solution would be to place kernel objects in DRAM's ZONE_NORMAL and not allow ZONE_NORMAL in non-DRAM. No objection on it. For large capacities, kernel object migratability might be a must. For capacities between moderate and large, kernel object migratibility or allowing ZONE_NORMAL in non-DRAM, or something better idea, would help to reduce ZONE_NORMAL cost. I'm adding my opinion with the last two cases in mind. Byungchul > I don't think the solution is to make kernel memory migratable and allow > kernel allocations on CXL. > > There's a reason most kernel allocations are not swappable. > > > Thanks, > > Honggyu
