Re: 2.6.20-ck1

Con Kolivas
2007-02-18T00:39:40Z

Andrew Morton writes:

> On Sun, 18 Feb 2007 08:00:06 +1100 Con Kolivas <kernel@kolivas.org> 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