On Wed, Oct 30, 2024 at 11:34:49AM -0700, John Hubbard wrote: > From a very high level design perspective, it's not yet clear to me > that there is either a "preferred" or "not recommended" aspect to > pinning in batches vs. all at once here, as long as one stays > below the type (int, long, unsigned...) limits of the API. Batching > seems like what you do if the internal implementation is crippled > and unable to meet its API requirements. So the fact that many > callers do batching is sort of "tail wags dog". No.. all things need to do batching because nothing should be storing a linear struct page array that is so enormous. That is going to create vmemap pressure that is not desirable. For instance rdma pins in batches and copies the pins into a scatter list and never has an allocation over PAGE_SIZE. iommufd transfers them into a radix tree. It is not so much that there is a limit, but that good kernel code just *shouldn't* be allocating gigantic contiguous memory arrays at all. Jason
