This has nothing to do with the "everything is a file" philosophy. It has to do with the fact that most *ix systems don't have a layer below them to do buffering. Actually even when you do the overhead of calling down to the driver for every write would kill some systems.
Think about a program that writes 80 bytes at a time to a large file. Each 80 byte write would involve going to VM each time. Suppose the block size is 4096 bytes (which is usually true) you would be doing 52 calls to VM without *ix buffering, while you only do one call to VM for each 4096 bytes with buffering. Reducing the number of calls to the driver by 52 times is a big win on some systems. There are other reasons for having the buffer cache embedded the way it is, but I don't want to get too long wended. -----Original Message----- From: Linux on 390 Port [mailto:[EMAIL PROTECTED] Behalf Of Phil Smith III Sent: Friday, September 17, 2004 4:13 AM To: [EMAIL PROTECTED] Subject: Re: Linux LPAR - how to drop caching Ranga Nathan <[EMAIL PROTECTED]> wrote: >We are on STK V2X DASD array. We can do very well without Linux adding >further caching. Is there a way to tell Linux not to cache the DASD? As David said, there's apparently no way to turn this off. For several years, I've been asking folks this same question. "You can't", they'd say. "But you keep saying, 'You can do anything, it's Linux!'", I'd respond. After saying that several times, I finally got an explanation that I think makes sense: this is a result of *ix's "everything is a file" philosophy. By the time the request gets down low enough in the OS that it hits the caching code, the fact that a page is from disk is long lost. That doesn't mean it couldn't be fixed (yes, I'm using the word "fixed" -- I see this as a serious design flaw, from a shared storage standpoint), just that it's non-trivial. HTH ...phsiii ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
