At this point, we're handling the majority of file-backed page faults under the VMA lock, using the ->map_pages entry point. This patch set attempts to expand that for the following siutations: - We have to do a read. This could be because we've hit the point in the readahead window where we need to kick off the next readahead, or because the page is simply not present in cache. - We're handling a write fault. Most applications don't do I/O by writes to shared mmaps for very good reasons, but some do, and it'd be nice to not make that slow unnecessarily. - We're doing a COW of a private mapping (both PTE already present and PTE not-present). These are two different codepaths and I handle both of them in this patch set. There is no support in this patch set for drivers to mark themselves as being VMA lock friendly; they could implement the ->map_pages vm_operation, but if they do, they would be the first. This is probably something we want to change at some point in the future, and I've marked where to make that change in the code. Suren, would you mind dropping this into your benchmarking setup and seeing if these relatively minor additions make a difference? Matthew Wilcox (Oracle) (6): mm: Make lock_folio_maybe_drop_mmap() VMA lock aware mm: Call wp_page_copy() under the VMA lock mm: Handle shared faults under the VMA lock mm: Handle COW faults under the VMA lock mm: Handle read faults under the VMA lock mm: Handle write faults to RO pages under the VMA lock mm/filemap.c | 13 ++++---- mm/memory.c | 93 ++++++++++++++++++++++++++++++++-------------------- 2 files changed, 65 insertions(+), 41 deletions(-) -- 2.40.1
