On Wed, Mar 12, 2025 at 08:38:07AM -0700, Suren Baghdasaryan wrote: > I might be wrong but my understanding is that we should try to > allocate from CMA when the allocation is movable (not pinned), so that > CMA can move those pages if necessary. I understand that in some cases > a movable allocation can be pinned and we don't know beforehand > whether it will be pinned or not. But in this case we know it will > happen and could avoid this situation. Any file or anonymous folio can be temporarily pinned for I/O and only moved once that completes. Direct I/O is one use case for that but there are plenty others. I'm not sure how you define "beforehand", but the pinning is visible in the _pincount field. > Yeah, low latency usecases for CMA are problematic and I think the > only current alternative (apart from solutions involving HW change) is > to use a memory carveouts. Device vendors hate that since carved-out > memory ends up poorly utilized. I'm working on a GCMA proposal which > hopefully can address that. I'd still like to understand what the use case is. Who does CMA allocation at a time where heavy direct I/O is in progress?
