Date: Fri, 30 Jul 1999 09:51:35 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Alan Cox <alc@cs.rice.edu> Cc: David Greenman <dg@root.com>, hackers@freebsd.org Subject: Re: patch for behavior changes and madvise MADV_DONTNEED Message-ID: <199907301651.JAA91354@apollo.backplane.com> References: <199907162234.PAA21850@apollo.backplane.com> <19990720014804.A21777@cs.rice.edu> <199907291856.LAA77471@apollo.backplane.com> <19990730000528.L10860@cs.rice.edu>
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:Your new "behavior" flag isn't known by vm_map_simply_entry, so
:map simplification could drop the behavior setting on the floor.
:I would prefer that the behavior is folded into eflags.
:
:Overall, I agree with the direction. Behavior is correctly a map
:attribute rather than an object attribute.
:
: Alan
:
:P.S. The MADV_FREE's by malloc/free were disabled by default in -CURRENT
:and -STABLE prior to the release of 3.2. They were a performance
:pessimization, slowing down "make world" by ~2%.
No problem, I think the behavior can easily be folded into eflags,
which deals with the map simplification code as well.
I'll work up a new patch.
-
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.
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.
-Matt
Matthew Dillon
<dillon@backplane.com>
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