linux-kernel - Re: 2.6.20-ck1

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Message-ID: <cone.1171759159.711805.13918.501@kolivas.org>
Date:	Sun, 18 Feb 2007 11:39:19 +1100
From:	Con Kolivas <kernel@...ivas.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Chuck Ebbert <cebbert@...hat.com>,
	michael chang <thenewme91@...il.com>,
	ck mailing list <ck@....kolivas.org>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.20-ck1

Andrew Morton writes:

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

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