Re: doubt about 99% of the cases if the first byte of the file is cached.

Unless there is a tux-devel list, I'd say it belongs here.  If there is 
a tux-devel list, I'd say it belongs on it.

Alex Kramarov wrote:
> I have been following this conversation for a long, long time, and though
> this is tux related, it doesn't seem that it belongs in this list. does
> anybody else feel the same ? maybe this should be private between the core
> tux developers and Liang ?
> 
> -------Original Message-------
> 
> From: [email protected]
> Date: Tuesday, April 23, 2002 19:04:20
> To: [email protected]
> Cc: [email protected]
> Subject: RE: doubt about 99% of the cases if the first byte of the file is
> cached.
> 
> Hi, Ingo
> 
> In our test case, we just build 10 files and each file is 5MB,10 files and
> each file is 10MB, 10 files and each file is 50MB. The main memory of
> TUX server is 256MB.
> 
> Why we build such big files for testing, the reason is we want linux to
> flush out those files when the cache limit is reached. So we can update
> caching status table in proxy.
> 
> We already test the feasibility of our project when we will use
> flush_inode_pages()
> in our program to flush a speicifc file. But now we want to get a real
> flush
> by Linux itself.
> 
> Now the question is can we know the maximum cache size of a backend
> server running Linux 2.4.18 if the main memory is 256MB?
> 
> BTW, we record the time for the request of a speicifc file in our test case.
> We found if the total size of all those http request files is bigger than
> 100MB, then the
> request time for a file again and again will be increased instead of
> decreased.
> So the performance of TUX is not improved because Linux take much time to
> swap between cache and disk.
> 
> But if the total size of all those http request files is less than 100MB,
> then the
> request time for a file again and again will be decreased. So the
> performance
> of TUX is improved because Linux already cached all these files in cache.
> 
> Is this result reasonable?
> 
> Liang
> 
> 
> 
> -----Original Message-----
> From: [email protected] [mailto:[email protected]]On Behalf Of Ingo Molnar
> Sent: Tuesday, April 23, 2002 7:43 AM
> To: Liang Yang
> Cc: [email protected]
> Subject: RE: doubt about 99% of the cases if the first byte of the file is
> cached.
> 
> 
> 
> On Tue, 23 Apr 2002, Liang Yang wrote:
> 
> 
>>But even we didn't enable noatime, LED should flash only for 1/10 second
>>or shorter time since Linux just need to update the access time flag of
>>this file. it is not a big job and it shouldn't take Linux a long time
>>to update this filed. But we noticed the Hard Disk LED flash for almost
>>2 seconds each time. So maybe Linux is doing some large amount hard disk
>>read/write operation instead of just updating file access time flag.
> 
> 
> well, is RAM large enough for all files accessed to be cached in RAM?
> 
> 
>>I guess for all the sizes of files, the access time flag should be the
>>same. Is that correct?
> 
> 
> yes, but each file has a different access flag, in different on-disk
> positions. So if you are accessing 100 files, the atime update sequence
> might create a longer LED flashing.
> 
> Ingo

-- 
Joe Cooper <[email protected]>
http://www.swelltech.com
Web Caching Appliances and Support