[mythtv-users] My MythTV journey

[Jarod C. Wilson]

On Dec 23, 2003, at 20:11, Brian Scully wrote:

>  --- On Tue 12/23, David Rees < drees at greenhydrant.com > wrote:
>
> On Tue, December 23, 2003 at 5:51 pm, Brian Scully wrote:
>>> I'm not sure why swap is being used then. I'm no kernel hacker, but 
>>> it
>>> seems strange that you would allow your cache to swap to disk - what
>>> performance benefit are you getting? BTW i'm up to 21 MB of swap 
>>> used now.
>
>> Linux will start swapping programs out to disk which haven't been 
>> used in
>> a while to make more room for filesystem cache.  Even if you have
>> gigabytes of memory in your machine, if you do a lot of work with 
>> large
>> files which exceed the amount of memory in the machine, the kernel 
>> will
>> start swapping some things out to improve performance.
>
> Agreed.  Jarod was suggesting that the kernel cached as much as 
> possible
> from disk reads to improve performance.

I never said anything at all about the kernel caching disk reads. I 
said:

"Linux will use up as much as your memory as it can. 512MB is plenty. 
I'm
sitting at a dual Athlon system with 1.5GB of RAM, not doing a huge 
amount of
stuff, and there isn't a huge amount of RAM "free". Everything gets 
cached to
memory for max performance. Again, 512MB is plenty (though I do 
recommend
more than 256MB, to avoid swapping). You aren't short on memory."

Nowhere in there does it say disk reads. :) Stuff that hasn't been 
accessed in some time might get swapped out, like David said, but I 
think I was misunderstood, and/or I misunderstood your original 
question. Long story short, 512MB of RAM is plenty for a MythTV box.

> The swapfile is on the disk.  My
> question was: if it is in fact the kernel's cache that is filling my 
> memory,
> Why would the kernel maintain that information on disk to save it from 
> being
> read from disk?  That was my original question.

It could be some program that was loaded into memory long ago, and 
hasn't been accessed in ages. Storing and fetching a program's memory 
out of swap is usually faster than killing and restarting the entire 
program.

-- 
Jarod C. Wilson, RHCE

Got a question? Read this first...
     http://catb.org/~esr/faqs/smart-questions.html
MythTV, Fedora Core & ATrpms documentation:
     http://wilsonet.com/mythtv/
MythTV Searchable Mailing List Archive
     http://www.gossamer-threads.com/archive/MythTV_C2/
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