Re: 2.6.20-ck1

[Con Kolivas <kernel@kolivas.org>]

Radoslaw Szkodzinski writes:

> On 2/18/07, Andrew Morton <akpm@linux-foundation.org> 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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-ck