linux-kernel - Re: [PATCH 3/3] Guarantee that COW faults for a process that called mmap(MAP

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Message-Id: <1211998534.12036.63.camel@localhost.localdomain>
Date:	Wed, 28 May 2008 13:15:34 -0500
From:	Adam Litke <agl@...ibm.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	akpm@...ux-foundation.org, dean@...tic.org,
	linux-kernel@...r.kernel.org, wli@...omorphy.com, dwg@....ibm.com,
	apw@...dowen.org, linux-mm@...ck.org, andi@...stfloor.org,
	kenchen@...gle.com, abh@...y.com, hannes@...urebad.de
Subject: Re: [PATCH 3/3] Guarantee that COW faults for a process that
	called mmap(MAP_PRIVATE) on hugetlbfs will succeed

On Wed, 2008-05-28 at 17:00 +0100, Mel Gorman wrote:
> [PATCH 4/3] Fix prio tree lookup
> 
> I spoke too soon. This is a fix to patch 3/3.
> 
> If a child unmaps the start of the VMA, the start address is different and
> that is perfectly legimite making the BUG_ON check bogus and should be removed.
> While page cache lookups are in HPAGE_SIZE, the vma->vm_pgoff is in PAGE_SIZE
> units, not HPAGE_SIZE. The offset calculation needs to be in PAGE_SIZE units
> to find other VMAs that are mapping the same range of pages. This patch
> fixes the offset calculation and adds an explanation comment as to why it
> is different from a page cache lookup.
> 
> Credit goes to Johannes Weiner for spotting the bogus BUG_ON on IRC which
> led to the discovery of the faulty offset calculation.
> 
> Signed-off-by: Mel Gorman <mel@....ul.ie>

Acked-by: Adam Litke <agl@...ibm.com>

-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center

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