linux-kernel - Re: [PATCH] hugetlb: call mmu notifiers on hugepage cow

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Message-Id: <20100603111125.8cd6a787.akpm@linux-foundation.org>
Date:	Thu, 3 Jun 2010 11:11:25 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Doug Doan <dougd@...y.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"lee.schermerhorn@...com" <lee.schermerhorn@...com>,
	"rientjes@...gle.com" <rientjes@...gle.com>,
	"mel@....ul.ie" <mel@....ul.ie>,
	Andrea Arcangeli <andrea@...hat.com>
Subject: Re: [PATCH] hugetlb: call mmu notifiers on hugepage cow

On Thu, 3 Jun 2010 10:36:00 -0700
Doug Doan <dougd@...y.com> wrote:

> > Well, specifically it means that
> > mmu_notifier_invalidate_range_start/end() implemetnations can no longer
> > take page_table_lock or any lock which nests outside page_table_lock.
> > That lessens flexibility.
> >
> > As the other mmu_notifier_invalidate_range_start/end() callsite in this
> > function carefully nested those calls outside page_table_lock, perhaps
> > that was thought to be a significant thing.
> 
> Here's my rationale: for the normal page case, the invalidation call is done 
> inside a page_table_lock,

It is?  Where does that happen?

> so the same should also be done in the huge page case. 
> Does it really make sense to call invalidation on one hugepage and have another 
> call invalidate the same hugepage while the first call is still not finished?
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