On Fri, Jul 30, 1999 at 09:51:35AM -0700, Matthew Dillon wrote: > > I'm not sure I see how MADV_FREE could slow performance down unless, > perhaps, it is the overhead of the system call itself. e.g. if malloc > is calling it on a page-by-page basis and not implementing any hysteresis. >
It's the system call overhead. Adding (more) hysteresis would reduce the overhead by some factor, but we'd still be making unnecessary MADV_FREE calls. Calling MADV_FREE accomplishes nothing unless the system is actually short of memory. The right way to address this problem is likely to add a mechanism to the VM system that sends a signal to the process when MADV_FREE would actually be beneficial. > 2% isn't a big deal. MADV_FREE theoretically makes a big impact on > paging performance in a heavily loaded & paging system. If your tests > were run on a system that wasn't paging, you weren't testing the right > thing. > 99% of our user base, whose machines aren't thrashing during a "make world" or other normal operation, shouldn't pay a 2% penalty to produce a theoretical improvement for the 1% that are. At best, that's "optimizing" the infrequent case at the expense of the frequent, not a good trade-off. In any case, the man page for malloc/free explains how to change the default, if you're a part of the "oppressed" 1%. Alan To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
