Re: [PATCH/RFC] Simplified Readahead

Steven Pratt
2004-09-27T21:05:19Z

Ray Bryant wrote:

> Hi Steve,
>
> On question I have (and I'm sorry, I haven't had time to look at your
> patch to sort this out) is what happens if the user supplies a rather
> serious I/O size, will you read ahead multiples of that, or what
> happens? Or, for that matter, how well will it perform?

Same behavior as the old code. I/Os are broken up into at most
max_readahead size pieces. In the case of the old code only 1 of these
could be outstanding. In the new code there could be at most 2
outstanding at any point in time.

>
> I've heard about HPC applications for IRIX that issue a 2GB read. :-)

This is why for these types of applications, especially on RAID arrays,
you need to set max_readahead into the MBs. (But that is a different topic).

Steve