Andrew Morton writes:
On Sun, 18 Feb 2007 08:00:06 +1100 Con Kolivas <[email protected]> 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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