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From: Christoph Lameter <cl@linux-foundation.org>
To: Andy Whitcroft <apw@shadowen.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Jon Tollefson <kniht@linux.vnet.ibm.com>,
	Mel Gorman <mel@csn.ul.ie>, Nick Piggin <nickpiggin@yahoo.com.au>
Subject: Re: [PATCH 1/1] hugetlbfs: handle pages higher order than MAX_ORDER
Date: Wed, 08 Oct 2008 11:17:59 -0500	[thread overview]
Message-ID: <48ECDD37.8050506@linux-foundation.org> (raw)
In-Reply-To: <1223458431-12640-2-git-send-email-apw@shadowen.org>

Andy Whitcroft wrote:
> When working with hugepages, hugetlbfs assumes that those hugepages
> are smaller than MAX_ORDER.  Specifically it assumes that the mem_map
> is contigious and uses that to optimise access to the elements of the
> mem_map that represent the hugepage.  Gigantic pages (such as 16GB pages
> on powerpc) by definition are of greater order than MAX_ORDER (larger
> than MAX_ORDER_NR_PAGES in size).  This means that we can no longer make
> use of the buddy alloctor guarentees for the contiguity of the mem_map,
> which ensures that the mem_map is at least contigious for maximmally
> aligned areas of MAX_ORDER_NR_PAGES pages.

But the memmap is contiguous in most cases. FLATMEM, VMEMMAP etc. Its only
some special sparsemem configurations that couldhave the issue because they
break up the vmemmap. x86_64 uses VMEMMAP by default. Is this for i386?


WARNING: multiple messages have this Message-ID (diff)
From: Christoph Lameter <cl@linux-foundation.org>
To: Andy Whitcroft <apw@shadowen.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Jon Tollefson <kniht@linux.vnet.ibm.com>,
	Mel Gorman <mel@csn.ul.ie>, Nick Piggin <nickpiggin@yahoo.com.au>
Subject: Re: [PATCH 1/1] hugetlbfs: handle pages higher order than MAX_ORDER
Date: Wed, 08 Oct 2008 11:17:59 -0500	[thread overview]
Message-ID: <48ECDD37.8050506@linux-foundation.org> (raw)
In-Reply-To: <1223458431-12640-2-git-send-email-apw@shadowen.org>

Andy Whitcroft wrote:
> When working with hugepages, hugetlbfs assumes that those hugepages
> are smaller than MAX_ORDER.  Specifically it assumes that the mem_map
> is contigious and uses that to optimise access to the elements of the
> mem_map that represent the hugepage.  Gigantic pages (such as 16GB pages
> on powerpc) by definition are of greater order than MAX_ORDER (larger
> than MAX_ORDER_NR_PAGES in size).  This means that we can no longer make
> use of the buddy alloctor guarentees for the contiguity of the mem_map,
> which ensures that the mem_map is at least contigious for maximmally
> aligned areas of MAX_ORDER_NR_PAGES pages.

But the memmap is contiguous in most cases. FLATMEM, VMEMMAP etc. Its only
some special sparsemem configurations that couldhave the issue because they
break up the vmemmap. x86_64 uses VMEMMAP by default. Is this for i386?

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  parent reply	other threads:[~2008-10-08 16:19 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-10-08  9:33 [PATCH 0/1] gigantic compound pages part 2 Andy Whitcroft
2008-10-08  9:33 ` Andy Whitcroft
2008-10-08  9:33 ` [PATCH 1/1] hugetlbfs: handle pages higher order than MAX_ORDER Andy Whitcroft
2008-10-08  9:33   ` Andy Whitcroft
2008-10-08 12:29   ` Nick Piggin
2008-10-08 12:29     ` Nick Piggin
2008-10-13 13:36     ` Andy Whitcroft
2008-10-13 13:36       ` Andy Whitcroft
2008-10-08 14:57   ` Mel Gorman
2008-10-08 14:57     ` Mel Gorman
2008-10-08 16:17   ` Christoph Lameter [this message]
2008-10-08 16:17     ` Christoph Lameter
2008-10-08 17:36     ` Andi Kleen
2008-10-08 17:36       ` Andi Kleen
2008-10-08 18:55     ` Andy Whitcroft
2008-10-08 18:55       ` Andy Whitcroft
2008-10-08 19:35       ` Christoph Lameter
2008-10-08 19:35         ` Christoph Lameter
2008-10-13 13:34         ` Andy Whitcroft
2008-10-13 13:34           ` Andy Whitcroft
2008-10-13 16:04           ` Christoph Lameter
2008-10-13 16:04             ` Christoph Lameter
2008-10-14  7:00             ` Andy Whitcroft
2008-10-14  7:00               ` Andy Whitcroft

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