Date: Thu, 17 Jan 2002 13:50:02 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: freebsd-bugs@FreeBSD.org Subject: Re: bin/33941: /usr/sbin/dev_mkdb dumps core Message-ID: <200201172150.g0HLo2s91348@freefall.freebsd.org>
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The following reply was made to PR bin/33941; it has been noted by GNATS.
From: Matthew Dillon <dillon@apollo.backplane.com>
To: Sheldon Hearn <sheldonh@starjuice.net>
Cc: Ryan Dooley <dooleyr@missouri.edu>, bug-followup@FreeBSD.ORG
Subject: Re: bin/33941: /usr/sbin/dev_mkdb dumps core
Date: Thu, 17 Jan 2002 13:41:53 -0800 (PST)
:On Thu, 17 Jan 2002 12:00:05 PST, Ryan Dooley wrote:
:
:> The only difference(s) are: (new vs. old where problem exists)
:>
:> 1) Generic Mach32 video card vs. 3Dfx Voodoo3 PCI video card,
:> 2) 128MB ram vs. 384MB ram, and
:> 3) generic newfs options vs. -b 32768 and -f 4096.
:
:I'd be _very_ careful trying a block size anything larger than 16384.
:I've heard horrible things about larger block sizes. I'm pretty sure
:Matt Dillon warned that >16384 block sizes would cause undesirable
:behaviour in the VM sysystem.
:
:Certainly, VM problems could account for your SEGV.
:
:Matt? Am I smoking crack, or did you say Very Bad Things about the VM
:system and block sizes >16384?
:
:Ciao,
:Sheldon.
It should work fine as long as the filesystem frag ratio is 8:1. The
buffer cache is optimized for 16384 byte buffers and can become
fragmented if larger block sizes are used, leading to inefficient
operation, but should have no other adverse effects. I would not use
a block size greater then 65536 though because you start to hit up
against internal limitations. Remember, the buffer cache has to reserve
KVA for each buffer, so the system's cache efficiency is going to drop
as the buffer size increases.
-Matt
Matthew Dillon
<dillon@backplane.com>
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