Re: linux os cache and ocfs

On Wed, 28 Jul 2004 05:41:28 -0700, utkanbir wrote:

> And most
> importantly , i use ocfs which uses direct io ,

It uses direct I/O only if you activate it and only if it is supported in kernel. You can activate direct I/O by setting the parameter filesystemio_options appropriately.

> so do i get any
> benefit of this linux disk cache? (since direct io does not use any os
> buffer )

Yes, you do. It's called "prefetch" and it does speed up access to the files that are mostly read only. Even more, Linux doesn't distinguish between data buffers in the buffer pool and page buffers. All modern Unix and Unix-like systems have blurred this distinction. Make no mistake, all Unix systems (and lookalikes) can support direct I/O, but doing so will usually cost you a penny or two. On Solaris, you should buy VxFS with QuickIO option. If you have 9.2.0.5 on Linux, you can use direct I/O against JFS file systems. Version 10 is scre...different.

> Why does linux incrase the cache size too much and than
> starts paging?

Let me rephrase the answer given to a similar question by Miss Jessica Rabbit, the consort of Roger Rabbit: Linux is not bad, it was just written that way.

> Whats the benefit of swapping ?

With swapping you can run many more simultaneous programs then without it. And, if you are not careful, swapping can easily kill the wabbit.

-- 
A city is a large community where people are lonesome together.