On Sat, Feb 01, 2025 at 11:30:24AM -0500, Gregory Price wrote: > Rather than ask whether we can make portions of the kernel more ammenable > to movable allocations, I think it's more beneficial to focus on whether > we can reduce the ZONE_NORMAL cost of ZONE_MOVABLE capacity. That seems > (to me) like the actual crux of this particular issue. We can! This is actually the topic of the talk I'm giving at FOSDEM in about 15 hours time. https://fosdem.org/2025/schedule/event/fosdem-2025-4860-shrinking-memmap/ I'm just going to run through my slides and upload them in an hour or so. My motivation isn't CXL related, but it's the sign of a good project that it solves some unrelated problems. Short version: we can halve the cost this year, halve it again in 2026 with a fairly managable amount of work, and maybe halve it a third time (for a total reduction of 7/8) with a lot more work in 2027. Further reductions beyond that are possible, but will need a lot more work. Some of that work we want to do anyway, regardless of whether the reduction in overhead from 16MB/GB to 2MB/GB is sufficient. ... or we'll discover the performance effect is negative and shelve the reduction in memmap size, having only accomplished a massive cleanup of kernel data structures. Which would be sad.
