Re: [PATCH] mm readahead: Fix sys_readahead breakage by reverting 2MB limit (bug 79111)

[Linus Torvalds]

On Thu, Jul 3, 2014 at 11:38 AM, Raghavendra K T
<raghavendra.kt@xxxxxxxxxxxxxxxxxx> wrote:
>
> Okay, how about something like 256MB? I would be happy to send a patch
> for that change.

I'd like to see some performance numbers. I know at least Fedora uses
"readahead()" in the startup scripts, do we have any performance
numbers for that?

Also, I think 256MB is actually excessive. People still do have really
slow devices out there. USB-2 is still common, and drives that read at
15MB/s are not unusual. Do we really want to do readahead() that can
take tens of seconds (and *will* take tens of seconds sycnhronously,
because the IO requests fill up).

So I wouldn't go from 2 to 256. That seems like an excessive jump. I
was more thinking in the 4-8MB range. But even then, I think we should
always have technical reasons (ie preferably numbers) for the change,
not just randomly change it.

           Linus
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