Return to BSD News archive
Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!news.mel.connect.com.au!munnari.OZ.AU!news.ecn.uoknor.edu!news.wildstar.net!serv.hinet.net!spring.edu.tw!voyager.iii.org.tw!nctuccca.edu.tw!howland.reston.ans.net!newsfeed.internetmci.com!in2.uu.net!news.artisoft.com!usenet
From: Terry Lambert <terry@lambert.org>
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: Linux vs. FreeBSD ... (FreeBSD extremely mem/swap hungry)
Date: Mon, 27 May 1996 12:44:27 -0700
Organization: Me
Lines: 41
Message-ID: <31AA061B.1914F01E@lambert.org>
References: <3188C1E2.45AE@onramp.net> <4o3ftc$4rc@zot.io.org> <31a9c16e.0@kaliban.csoma.elte.hu>
NNTP-Posting-Host: hecate.artisoft.com
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Mailer: Mozilla 2.01 (X11; I; Linux 1.1.76 i486)
Ingo Molnar wrote:
] : What's wasteful is that Linux has all this high speed access RAM
] : (physical memory) and all this medium speed access RAM (swap) and
] : all this low speed access RAM (the disk, and the program images
] : being used as swap store), and it is preferentially discarding
] : perfectly good medium speed access pages in favor of low speed
] : access pages and making the numbers you are misinterpreting look
] : "good".
]
] the filesystem is "medium speed" on Linux. You can read/write
] files at disk hardware speed under ext2fs (using the proper
] busmastering hardware). Linux isnt swapping code too good, it's
] rather for swapping >data<, not code. Linux is optimized for
] "random data access", if we talk about swapping. There is no
] readahead in the swap space AFAIR. (there was some discussion
] about sequential data swapping used in many scientific
] calculations, but there is no code in the kernel yet) A well-
] installed filesystem has properly placed files, there is very
] low overhead in reading them.
But, you must admit, the overhead is higher reading a block
from a file in a filesystem (even ext2fs) because reading a
raw block from a device offset is faster than reading a file
block from a file offset.
In any case, if you call file access "medium speed", then there
is still some "faster than medium speed" I/O that can be done
(and isn't done).
This is not to denigrate Linux; it's simply to point out that
the VM numbers he was claiming were "bad" didn't mean what he
thought they meant.
Terry Lambert
terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.