Re: [PATCH 2/3] mm: make the threshold of enabling THP configurable

From: Cong Wang
Date: Wed Jun 22 2011 - 08:35:11 EST

ä 2011å06æ22æ 19:15, Mel Gorman åé:
On Wed, Jun 22, 2011 at 06:46:39PM +0800, Cong Wang wrote:
??? 2011???06???22??? 17:16, Mel Gorman ??????:

What I meant was that there is a rational reason why 512M is the
default for enabling THP by default. Tuning it lower than that by any
means makes very little sense. Tuning it higher might make some sense
but it is more likely that THP would simply be disabled via sysctl. I
see very little advantage to introducing this Kconfig option other
than as a source of confusion when running make oldconfig.

The tunable range is (512, 8192), so 512M is the minimum.

Sure, I knew it can be disabled via /sys, actually we can do even
more in user-space, that is totally move the 512M check out of kernel,
why we didn't?

Because the reason why 512M is the default is not obvious and there
was no guarantee all distros would chose a reasonable default for
an init script (or know that an init script was even necessary).
This is one of the few cases where there is a sensible default that
is the least surprising.

Putting a well-explained Kconfig help would solve this problem,
so I don't think this is a surprising thing.
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