On Wed, 23 Oct 2002 16:44:06 +1000 (EST), Bruce Evans <[EMAIL PROTECTED]> said:
bde> I should be the last to defend the current design and implementation of bde> the buffer cache, since I think it gets almost everything wrong (the bde> implementation is OK, but has vast complications to work around design bde> errors), but I think buffer_map is one of the things that it gets right bde> (if we're going to have buffers at all). (snip) bde> I use the following changes in -current to enlarge the buffer cache and bde> avoid fragmentation. These only work because I don't have much physical bde> memory (512MB max). Even i386's have enough vm for the pure form of bde> buffer_map to work: bde> - enlarge BKVASIZE to MAXBSIZE so that fragmentation can not (should not?) bde> occur. bde> - enlarge nbuf by a factor of (my_BKVASIZE / current_BKVASIZE) to work bde> around bugs. The point of BKVASIZE got lost somewhere. bde> - enlarge nbuf and associated variables by another factor of 2 or 4 to bde> get a larger buffer cache. bde> This is marginal for 512MB physical, and probably wouldn't work if I had bde> a lot of mbufs. nbuf is about 4000 and buffer_map takes about 256MB. bde> 256MB is a lot, but nbuf = 4000 isn't a lot. I used buffer caches bde> with 2000 * 1K buffers under Minix and Linux before FreeBSD, and ISTR bde> having an nbuf of 5000 or so in FreeBSD-1.1. At least 2880 buffers are bde> needed to properly cache a tiny 1.44MB floppy with an msdosfs file bde> system with a block size of 512, and that was an important test case. bde> End of FreeBSD-[2-5] history. Incidentally, Solaris 7 on sun4u reserves a space of 256MB in the KVM according to Solaris Internals. On i386 (x86), the size is only 4MB. Not sure whether they use those spaces in a pure form, or they cluster some consecutive pages (which leads to fragmentation), though... NetBSD UBC also makes a map dedicated to buffers in kernel_map. Maybe there is a point to have a map dedicated to the buffer space for a better stability, and the size of the buffer map could be much smaller than now. During my testing, I found that only up to 6-7MB of the buffers out of 40-50MB were wired down (ie busy, locked for background write or dirty) at most. -- Seigo Tanimura <[EMAIL PROTECTED]> To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-current" in the body of the message
