On Wed, 5 Mar 2025 20:49:13 +0100 David Hildenbrand <david@xxxxxxxxxx> wrote: > On 05.03.25 20:46, 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. Shakeel is correct. Thank you for making the early clarification Shakeel. Also sorry for causing confuses. I will make this point clearer on next spin. > > Makes a lot of sense to me! Seems Shakeel already addressed all question so far, but please feel free to raise more question for anything not yet cleared! > > -- > Cheers, > > David / dhildenb Thanks, SJ
