On Wed, Mar 05, 2025 at 11:46:31AM -0800, Shakeel Butt wrote: > On Wed, Mar 05, 2025 at 08:19:41PM +0100, David Hildenbrand wrote: > > On 05.03.25 19:56, Matthew Wilcox wrote: > > > On Wed, Mar 05, 2025 at 10:15:55AM -0800, SeongJae Park wrote: > > > > For MADV_DONTNEED[_LOCKED] or MADV_FREE madvise requests, tlb flushes > > > > can happen for each vma of the given address ranges. Because such tlb > > > > flushes are for address ranges of same process, doing those in a batch > > > > is more efficient while still being safe. Modify madvise() and > > > > process_madvise() entry level code path to do such batched tlb flushes, > > > > while the internal unmap logics do only gathering of the tlb entries to > > > > flush. > > > > > > Do real applications actually do madvise requests that span multiple > > > VMAs? It just seems weird to me. Like, each vma comes from a separate > > > call to mmap [1], so why would it make sense for an application to > > > call madvise() across a VMA boundary? > > > > I had the same question. If this happens in an app, I would assume that a > > single MADV_DONTNEED call would usually not span multiples VMAs, and if it > > does, not that many (and that often) that we would really care about it. > > IMHO madvise() is just an add-on and the real motivation behind this > series is your next point. > > > > > OTOH, optimizing tlb flushing when using a vectored MADV_DONTNEED version > > would make more sense to me. I don't recall if process_madvise() allows for > > that already, and if it does, is this series primarily tackling optimizing > > that? > > Yes process_madvise() allows that and that is what SJ has benchmarked > and reported in the cover letter. In addition, we are adding > process_madvise() support in jemalloc which will land soon. > Feels like me adjusting that to allow for batched usage for guard regions has opened up unexpected avenues, which is really cool to see :) I presume the usage is intended for PIDFD_SELF usage right? At some point we need to look at allowing larger iovec size. This was something I was planning to look at at some point, but my workload is really overwhelming + that's low priority for me so happy for you guys to handle that if you want. Can discuss at lsf if you guys will be there also :)
