Re: [patch 12/18] hugetlbfs: support larger than MAX_ORDER

[Nishanth Aravamudan <nacc@us.ibm.com>]

On 23.04.2008 [11:53:14 +1000], npiggin@suse.de wrote:
> This is needed on x86-64 to handle GB pages in hugetlbfs, because it is
> not practical to enlarge MAX_ORDER to 1GB. 
> 
> Instead the 1GB pages are only allocated at boot using the bootmem
> allocator using the hugepages=... option.
> 
> These 1G bootmem pages are never freed. In theory it would be possible
> to implement that with some complications, but since it would be a one-way
> street (>= MAX_ORDER pages cannot be allocated later) I decided not to
> currently.
> 
> The >= MAX_ORDER code is not ifdef'ed per architecture. It is not very big
> and the ifdef uglyness seemed not be worth it.
> 
> Known problems: /proc/meminfo and "free" do not display the memory 
> allocated for gb pages in "Total". This is a little confusing for the
> user.
> 
> Signed-off-by: Andi Kleen <ak@suse.de>
> Signed-off-by: Nick Piggin <npiggin@suse.de>
> ---
>  mm/hugetlb.c |   74 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 72 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6/mm/hugetlb.c
> ===================================================================
> --- linux-2.6.orig/mm/hugetlb.c
> +++ linux-2.6/mm/hugetlb.c
> @@ -14,6 +14,7 @@
>  #include <linux/mempolicy.h>
>  #include <linux/cpuset.h>
>  #include <linux/mutex.h>
> +#include <linux/bootmem.h>
> 
>  #include <asm/page.h>
>  #include <asm/pgtable.h>
> @@ -160,7 +161,7 @@ static void free_huge_page(struct page *
>  	INIT_LIST_HEAD(&page->lru);
> 
>  	spin_lock(&hugetlb_lock);
> -	if (h->surplus_huge_pages_node[nid]) {
> +	if (h->surplus_huge_pages_node[nid] && h->order < MAX_ORDER) {

Shouldn't all h->order accesses actually be using the huge_page_order()
to be consistent?

Thanks,
Nish

-- 
Nishanth Aravamudan <nacc@us.ibm.com>
IBM Linux Technology Center

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