Re: 2.6.20-ck1

[Con Kolivas]

Radoslaw Szkodzinski writes:

> 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:
> >
> >         MAX_PAGECACHE=4M MAX_DIRTY_PAGECACHE=2M rsync foo bar
> >
> > 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.

Hey Radoslaw, your points are valid but Andrew was referring to the tail 
large files patch in this email.

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