where did all my memory go? (file system cache)

[Chris Hodgins]

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