On Wed, Jan 2, 2013 at 8:50 AM, Roman Dubtsov <[email protected]> wrote: > Concurrent mmap() calls from the same process are serialized via downing > mm->mmap_sem for write. This means that operations like populating the > pages which do not alter vmas are also performed serially. Anecdotal > data from two machines I have access to is that populating pages by > touching them in a loop outside of mmap() improves performance of the > synthetic micro-benchmark by ~40% in the worst case. A crude patch that > modifies vm_mmap_pgoff() to call make_pages_present() outside of > do_mmap_pgoff() after upping the semaphore when MAP_POPULATE is present > brings identical performance improvement. > > Is there an interest in fixing this or concurrent mmaps() from the same > process are too much of a corner case to worry about it?
Funny this comes up again. I actually have a patch series that is supposed to do that: [PATCH 0/9] Avoid populating unbounded num of ptes with mmap_sem held However, the patches are still pending, didn't get much review (probably not enough for Andrew to take them at this point), and I think everyone forgot about them during the winter break. Care to have a look at that thread and see if it works for you ? (caveat: you will possibly also need "[PATCH 10/9] mm: make do_mmap_pgoff return populate as a size in bytes, not as a bool" to make the series actually work for you) -- Michel "Walken" Lespinasse A program is never fully debugged until the last user dies. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
