linux-kernel - Re: oops in copy_page

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Date:	Sun, 6 Jan 2013 19:38:35 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	Dave Jones <davej@...hat.com>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: oops in copy_page_rep()

On Sun, 6 Jan 2013, Dave Jones wrote:
> 
> investigating the huge page theory a little further I'm a bit confused.
> The kernel on that machine has THP enabled, and the cpu supports it (an old amd64), but..
> 
> $ cat /sys/kernel/mm/hugepages/hugepages-2048kB/*
> 0
> 0
> 0
> 0
> 0
> 0
> 
> I was expecting at least one of those to be non-zero.
> 
> /sys/kernel/mm/transparent_hugepage/khugepaged/full_scans and pages_collapsed
> are both non-zero, so it's been busy doing _something_.
> 
> Is this expected behaviour ?

Yes.  /sys/kernel/mm/hugepages/ is all about those dusty old opaque
hugepages you might have got from fs/hugetlbfs and mm/hugetlb.c; whereas
the splitting issue we suspect is peculiar to the dazzling new transparent
hugepages you get from mm/huge_memory.c.

Hugh
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