Re: 2.6.20-ck1

[Con Kolivas]

Andrew Morton writes:

> On Sun, 18 Feb 2007 08:00:06 +1100 Con Kolivas <kernel@xxxxxxxxxxx> wrote:
>
> > On Sunday 18 February 2007 05:45, Chuck Ebbert wrote:
> > ...
> > > But the one I like, mm-filesize_dependant_lru_cache_add.patch,
> > > has an on-off switch.
> > >
> >
> > ...
> >
> > Do you still want this patch for mainline?... 
>
> Don't think so.  The problems I see are:
>
> - It's a system-wide knob.  In many situations this will do the wrong
>   thing.  Controlling pagecache should be per-process.
>
> - Its heuristics for working out when to invalidate the pagecache will be
>   too much for some situations and too little for others.
>
> - Whatever we do, there will be some applications in some situations
>   which are hurt badly by changes like this: they'll do heaps of extra IO.
>
>
> 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.

Rest assured I wasn't interested in pushing this patch for mainline anyway.

-ck users can also rest assured about this patch for the following reasons:

- The usage pattern on a desktop will guarantee that this patch helps 99.9% 
of the time rather than hurts. Therefore, this feature is enabled by default 
on -ck.

- With the usage pattern on a server of any sort, it will be unknown whether 
this patch helps or harms. Therefore, this feature is disabled by default on 
-cks.

--
-ck

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