mmap vs. O_DIRECT

Bill Davidsen
2004-11-10T20:21:49Z

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