linux-kernel - Re: [PATCH] hugetlb: Fix pool resizing corner case

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Message-ID: <b040c32a0710031208s5323d16ao47becace88c2bc79@mail.gmail.com>
Date:	Wed, 3 Oct 2007 12:08:52 -0700
From:	"Ken Chen" <kenchen@...gle.com>
To:	"Dave Hansen" <haveblue@...ibm.com>
Cc:	"Adam Litke" <agl@...ibm.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hugetlb: Fix pool resizing corner case

On 10/3/07, Dave Hansen <haveblue@...ibm.com> wrote:
> > Not quite.  Count can never go below the number of reserved pages plus
> > pages allocated to MAP_PRIVATE mappings.  That number is computed by:
> > (resv + (total - free)).
>
> So, (total - free) equals the number of MAP_PRIVATE pages?  Does that
> imply that all reserved pages are shared and that all shared pages are
> reserved?

no, not quite.  In-use huge page (total - free) can be both private or
shared.  resv_huge_pages counts number of pages that is committed for
shared mapping, but not yet faulted in.

What the equation does essentially is: resv_huge_pages + nr-huge-pages-in-use.

- Ken
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