Date: Thu, 17 Feb 2005 01:55:25 +0000 From: Chris Hodgins <chodgins@cis.strath.ac.uk> To: Julian Elischer <julian@elischer.org> Cc: current@freebsd.org Subject: Re: where did all my memory go? (file system cache) Message-ID: <4213F98D.7020304@cis.strath.ac.uk> In-Reply-To: <4213D3AA.70809@elischer.org> References: <1108584730.95661.12.camel@server.mcneil.com> <20050216201716.GA28436@odin.ac.hmc.edu> <4213B3C8.3090508@centtech.com> <1108588393.12275.9.camel@server.mcneil.com> <20050216214031.GA2787@odin.ac.hmc.edu> <4213D3AA.70809@elischer.org>
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Julian Elischer wrote:
> slightly off topic but..
>
> Brooks Davis wrote:
>
>> On Wed, Feb 16, 2005 at 01:13:13PM -0800, Sean McNeil wrote:
>>
>>
>> The concept that most of your memory should be entierly free when the
>> system is not under load is simply wrong. The simplistic world view of
>> memory being allocated to a specific task or entierly free simply isn't
>> correct for all that it makes for nice graphs anyone can pretend they
>> understand. You can produce some sort of aproximation of the output you
>> see on other systems by modifying the program to include inactive memory
>> in free memory. That's what I did with Ganglia.
>>
>
> what I really want is a way to FORce certain pages out of cache.
> In particular I need to verify teh correctness of the version on 2ndary
> storage..
>
> what I want is:
>
> int fd = open("myfile",...);
> write1GBfiletodisk(fd, data);
> ioctl(fd, PURGEFROMCACHE);
> perform_md5(fd);
>
> and be sure that teh MD5 is that of what is on the disk.
> not what is in RAM.
>
>>
>> -- Brooks
>>
>>
>>
>
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>
IANAE but could you not use the O_DIRECT flag with open?
O_DIRECT eliminate or reduce cache effects
HTH
Chris
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