Nick Piggin wrote: > Cool. According to my thinking, madvise(MADV_DONTNEED) even in today's > kernels using down_write(mmap_sem) for MADV_DONTNEED is better than > mmap/mprotect, which have more fundamental locking requirements, more > overhead and no benefits (except debugging, I suppose).
It's a tiny bit faster, see http://people.redhat.com/drepper/dontneed.png I just ran it once so the graph is not smooth. This is on a UP dual core machine. Maybe tomorrow I'll turn on the big 4p machine. I would have to see dramatically different results on the big machine to make me change the libc code. The reason is that there is a big drawback. So far, when we allocate a new arena, we allocate address space with PROT_NONE and only when we need memory the protection is changed to PROT_READ|PROT_WRITE. This is the advantage of catching wild pointer accesses. -- ➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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