On 10/13/18 9:47 AM, Christoph Hellwig wrote: > On Sat, Oct 13, 2018 at 12:34:12AM -0700, John Hubbard wrote: >> In patch 6/6, pin_page_for_dma(), which is called at the end of get_user_pages(), >> unceremoniously rips the pages out of the LRU, as a prerequisite to using >> either of the page->dma_pinned_* fields. >> >> The idea is that LRU is not especially useful for this situation anyway, >> so we'll just make it one or the other: either a page is dma-pinned, and >> just hanging out doing RDMA most likely (and LRU is less meaningful during that >> time), or it's possibly on an LRU list. > > Have you done any benchmarking what this does to direct I/O performance, > especially for small I/O directly to a (fast) block device? Not yet. I can go do that now. If you have any particular test suites, benchmarks, or just programs to recommend, please let me know. So far, I see tools/testing/selftests/vm/gup_benchmark.c -- thanks, John Hubbard NVIDIA
