Re: [ck] Re: 2.6.20-ck1

From: Radoslaw Szkodzinski
Date: Sat Feb 17 2007 - 19:41:26 EST

On 2/18/07, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
Generally, the penalties for getting this stuff wrong are very very high:
orders of magnitude slowdowns in the right situations. Which I suspect
will make any system-wide knob ultimately unsuccessful.

Yes, they were. Now, it's an extremely light and well-tuned patch.
kprefetchd should only run on a totally idle system now.

The ideal way of getting this *right* is to change every application in the
world to get smart about using sync_page_range() and/or posix_fadvise(),
then to add a set of command-line options to each application in the world
so the user can control its pagecache handling.

We don't live in a perfect world. :-)

Obviously that isn't practical. But what _could_ be done is to put these
pagecache smarts into glibc's read() and write() code. So the user can do:


This will provide pagecache control for pretty much every application. It
has limitations (fork+exec behaviour??) but will be useful.

Not too useful for interactive applications with unpredictable memory
consumption behaviour, where swap-prefetch still helps.

A kernel-based solution might use new rlimits, but would not be as flexible
or successful as a libc-based one, I suspect.
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