mmap vs. O_DIRECT

[Bill Davidsen <davidsen@tmr.com>]

I have an application which does a lot of mmap to process its data. The 
huge waitio time makes me think that mmap isn't doing direct i/o even 
when things are alligned. Before I start poking the code, is there a 
reason why direct is not default for i/o in page-size transfers on page 
size file offsets? I don't have source code, but the parameters of the 
mmap all seem to satisfy the allignment requirements.

I realize there may be a reason for forcing the i/o through kernel 
buffers, or for not taking advantage of doing direct i/o whenever 
possible, it just doesn't jump out at me.

-- 
    -bill davidsen (davidsen@tmr.com)
"The secret to procrastination is to put things off until the
  last possible moment - but no longer"  -me