Date: Mon, 19 Jun 1995 11:31:57 -0700 From: John Dyson <dyson@Root.COM> To: freebsd-hackers@freebsd.org, graichen@sirius.physik.fu-berlin.de Subject: Re: freebsd and memory Message-ID: <199506191831.LAA05790@Root.COM>
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FreeBSD uses both a buffer cache and a VM cache. It is probably using more than 3MB for its buffer cache on a 16MB system. The kernel data structures on FreeBSD are not small either. Note also that FreeBSD does NOT defer updates to filesystem metadata. Linux does -- so it is more possible to have stale metadata on a Linux disk. FreeBSD also starts filesystem writes almost immediately when a file is written to (actually when a cluster is completed.) I think that Linux waits until a sync occurs (or the "sync" daemon runs.) I have been pondering the relative merits of different policies for filesystem I/O. Some experiments that I have run show that if the data needs to be non-volatile on the disk that the system is faster to do the I/O like FreeBSD does. If the data is volatile, it appears to be faster to do the I/O like Linux does. (These are just heuristic type off-the-cuff observations.) John dyson@root.com
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