From owner-freebsd-hackers Sun Sep 23 14: 9:58 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from earth.backplane.com (earth-nat-cw.backplane.com [208.161.114.67]) by hub.freebsd.org (Postfix) with ESMTP id 9287C37B41E for ; Sun, 23 Sep 2001 14:09:54 -0700 (PDT) Received: (from dillon@localhost) by earth.backplane.com (8.11.6/8.11.2) id f8NL9kU88657; Sun, 23 Sep 2001 14:09:46 -0700 (PDT) (envelope-from dillon) Date: Sun, 23 Sep 2001 14:09:46 -0700 (PDT) From: Matt Dillon Message-Id: <200109232109.f8NL9kU88657@earth.backplane.com> To: Wilko Bulte Cc: Poul-Henning Kamp , David Greenman , Seigo Tanimura , bright@wintelcom.net, hackers@FreeBSD.ORG Subject: Re: Conclusions on... was Re: More on the cache_purgeleafdirs() routine References: <96469.1001237641@critter> <200109231040.f8NAeXw86352@earth.backplane.com> <20010923124702.B9914@freebie.xs4all.nl> Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG :Has the problem of small-memory machines (< 64M IIRC) solved now? As I :understand it vmiodirenable is counter-productive for these boxes. :Maybe one could decide on-boot whether the amount of mem is enough to :make it useful? : :Just a thought of course. : :| / o / /_ _ email: wilko@FreeBSD.org Small memory machines never had a problem. Even though there can be considerable memory inefficiencies using vmiodirenable (e.g. a directory less then 512 bytes eats 512 bytes of physical ram with vmiodirenable turned off, and 4K with it turned on), there are two compensating factors: First, the VM Paging cache is a cache, so the cached directory blocks can be thrown away. Second, the VM Page cache has all of memory to play with while the buffer cache with vmiodirenable turned off on a 64MB machine will reserve less then a megabyte to cache directories. #2 is important because it leads to more I/O which has a far greater effect on the system then memory waste. Also, if you look at the typical program's memory footprint and assume that actively accessed directories eat 4K, the memory used to hold the active directories winds up being almost nothing compared to the RSS of the program using those directories. Single-use directories (e.g. make buildworld) are recycled in the VM Page cache and do not eat as much memory as you might otherwise think. So even though the memory inefficiency can be up to 8:1 (4096/512), this factor is somewhat deceptive in regards to the actual effect on the system. -Matt To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message