Message-ID: <4DFF7CDD.308@redhat.com>
Date: Tue, 21 Jun 2011 01:01:17 +0800
From: Cong Wang <amwang@redhat.com>
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To: Andrea Arcangeli <aarcange@redhat.com>
CC: linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        Rik van Riel <riel@redhat.com>, Johannes Weiner <jweiner@redhat.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, linux-mm@kvack.org
Subject: Re: [PATCH 1/3] mm: completely disable THP by transparent_hugepage=never
References: <1308587683-2555-1-git-send-email-amwang@redhat.com> <20110620165035.GE20843@redhat.com>
In-Reply-To: <20110620165035.GE20843@redhat.com>
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于 2011年06月21日 00:50, Andrea Arcangeli 写道:
> 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
> /dev/mem.


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/
exists.

>
> 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.

Thanks.
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