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? Regards, Roma -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
