Re: [PATCH 1/3] mm: completely disable THP by transparent_hugepage=never

From: Cong Wang
Date: Mon Jun 20 2011 - 13:01:58 EST

ä 2011å06æ21æ 00:50, Andrea Arcangeli åé:
On Tue, Jun 21, 2011 at 12:34:28AM +0800, Amerigo Wang wrote:
transparent_hugepage=never should mean to disable THP completely,
otherwise we don't have a way to disable THP completely.
The design is broken.

We want to allow people to boot with transparent_hugepage=never but to
still allow people to enable it later at runtime. Not sure why you
find it broken... Your patch is just crippling down the feature with
no gain. There is absolutely no gain to disallow root to enable THP
later at runtime with sysfs, root can enable it anyway by writing into

What can I do if I don't want to see THP at all? I mean the same
behavior as when my CPU doesn't have PSE.

With this patch, there is no even /sys/kernel/vm/transparent_hugepage/

Unless you're root and you enable it, it's completely disabled, so I
don't see what you mean it's not completely disabled. Not even
khugepaged is started, try to grep of khugepaged... (that wouldn't be
the same with ksm where ksm daemon runs even when it's off for no
gain, but I explicitly solved the locking so khugepaged will go away
when enabled=never and return when enabled=always).

Without this patch, THP is still initialized (although khugepaged is not started),
that is what I don't want to see when I pass "transparent_hugepage=never",
because "never" for me means THP is totally unseen, even not initialized.

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