Date: Sun, 5 Jul 2009 10:00:44 +0200 From: Gary Jennejohn <gary.jennejohn@freenet.de> To: Alexander Motin <mav@FreeBSD.org> Cc: freebsd-arch@freebsd.org Subject: Re: DFLTPHYS vs MAXPHYS Message-ID: <20090705100044.4053e2f9@ernst.jennejohn.org> In-Reply-To: <4A4FAA2D.3020409@FreeBSD.org> References: <4A4FAA2D.3020409@FreeBSD.org>
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On Sat, 04 Jul 2009 22:14:53 +0300 Alexander Motin <mav@FreeBSD.org> wrote: > Can somebody explain me a difference between DFLTPHYS and MAXPHYS > constants? As I understand, the last one is a maximal amount of memory, > that can be mapped to the kernel, or passed to the hardware drivers. But > why then DFLTPHYS is used in so many places and what does it mean? > There's a pretty good comment on these in /sys/conf/NOTES. > Isn't it a time to review their values for increasing? 64KB looks funny, > comparing to modern memory sizes and data rates. It just increases > interrupt rates, but I don't think it really need to be so small to > improve interactivity now. > Probably historical from the days when memory was scarce. There's nothing preventing the user from upping these values in his kernel config file. But note the warning in NOTES about possibly making the kernel unbootable. It's not clear whether this warning is still valid given todays larger memory footprints and the inmproved VM system. I wonder whether all drivers can correctly handle larger values for DFLTPHYS. --- Gary Jennejohn
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