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Message-Id: <20091030094037.9e0118d8.kamezawa.hiroyu@jp.fujitsu.com>
Date: Fri, 30 Oct 2009 09:40:37 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Andrea Arcangeli <aarcange@...hat.com>
Cc: Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
linux-mm@...ck.org, Marcelo Tosatti <mtosatti@...hat.com>,
Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
Izik Eidus <ieidus@...hat.com>,
Hugh Dickins <hugh.dickins@...cali.co.uk>,
Nick Piggin <npiggin@...e.de>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org
Subject: Re: RFC: Transparent Hugepage support
On Thu, 29 Oct 2009 11:36:58 +0100
Andrea Arcangeli <aarcange@...hat.com> wrote:
> > A small comment regarding the patch itself: i think it could be
> > simplified further by eliminating CONFIG_TRANSPARENT_HUGEPAGE and by
> > making it a natural feature of hugepage support. If the code is correct
> > i cannot see any scenario under which i wouldnt want a hugepage enabled
> > kernel i'm booting to not have transparent hugepage support as well.
>
> The two reasons why I added a config option are:
>
> 1) because it was easy enough, gcc is smart enough to eliminate the
> external calls so I didn't need to add ifdefs with the exception of
> returning 0 from pmd_trans_huge and pmd_trans_frozen. I only had to
> make the exports of huge_memory.c visible unconditionally so it doesn't
> warn, after that I don't need to build and link huge_memory.o.
>
> 2) to avoid breaking build of archs not implementing pmd_trans_huge
> and that may never be able to take advantage of it
>
> But we could move CONFIG_TRANSPARENT_HUGEPAGE to an arch define forced
> to Y on x86-64 and N on power.
Ah, please keep CONFIG_TRANSPARENT_HUGEPAGE for a while.
Now, memcg don't handle hugetlbfs because it's special and cannot be freed by
the kernel, only users can free it. But this new transparent-hugepage seems to
be designed as that the kernel can free it for memory reclaiming.
So, I'd like to handle this in memcg transparently.
But it seems I need several changes to support this new rule.
I'm glad if this new huge page depends on !CONFIG_CGROUP_MEM_RES_CTRL for a
while.
Thanks,
-Kame
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