linux-kernel - Re: Hugepage regression

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Date:	Tue, 10 Oct 2006 02:04:26 -0700
From:	Andrew Morton <akpm@...l.org>
To:	David Gibson <david@...son.dropbear.id.au>
Cc:	Chen@...abs.org, Kenneth W <kenneth.w.chen@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Hugepage regression

On Tue, 10 Oct 2006 18:47:48 +1000
David Gibson <david@...son.dropbear.id.au> wrote:

> It seems commit fe1668ae5bf0145014c71797febd9ad5670d5d05 causes a
> hugepage regression.  A git bisect points the finger at that commit
> for causing an oops in the 'alloc-instantiate-race' test from the
> libhugetlbfs testsuite.
> 
> Still looking to determine the reason it breaks things.
> 

It's assuming that unmap_hugepage_range() is always freeing these pages. 
If the page is shared by another mapping, bad things will happen: the
threads fight over page->lru.

Doing

+	if (page_count(page) == 1)
		list_add(&page->lru, &page_list);

might help.  But then we miss the tlb flush in rare racy conditions.
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