linux-kernel - Re: [PATCH 1/1] hugetlb: pull gigantic page initialisation out of the default path

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Message-Id: <200810082331.45359.nickpiggin@yahoo.com.au>
Date:	Wed, 8 Oct 2008 23:31:45 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Andy Whitcroft <apw@...dowen.org>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Jon Tollefson <kniht@...ux.vnet.ibm.com>,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH 1/1] hugetlb: pull gigantic page initialisation out of the default path

On Wednesday 08 October 2008 20:34, Andy Whitcroft wrote:
> As we can determine exactly when a gigantic page is in use we can optimise
> the common regular page cases by pulling out gigantic page initialisation
> into its own function.  As gigantic pages are never released to buddy we
> do not need a destructor.  This effectivly reverts the previous change
> to the main buddy allocator.  It also adds a paranoid check to ensure we
> never release gigantic pages from hugetlbfs to the main buddy.

Thanks for doing this. Can prep_compound_gigantic_page be #ifdef HUGETLB?


> Signed-off-by: Andy Whitcroft <apw@...dowen.org>
> Cc: Nick Piggin <nickpiggin@...oo.com.au>
> ---
>  mm/hugetlb.c    |    4 +++-
>  mm/internal.h   |    1 +
>  mm/page_alloc.c |   26 +++++++++++++++++++-------
>  3 files changed, 23 insertions(+), 8 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index bb5cf81..716b151 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -460,6 +460,8 @@ static void update_and_free_page(struct hstate *h,
> struct page *page) {
>  	int i;
>
> +	BUG_ON(h->order >= MAX_ORDER);
> +
>  	h->nr_huge_pages--;
>  	h->nr_huge_pages_node[page_to_nid(page)]--;
>  	for (i = 0; i < pages_per_huge_page(h); i++) {
> @@ -984,7 +986,7 @@ static void __init gather_bootmem_prealloc(void)
>  		struct hstate *h = m->hstate;
>  		__ClearPageReserved(page);
>  		WARN_ON(page_count(page) != 1);
> -		prep_compound_page(page, h->order);
> +		prep_compound_gigantic_page(page, h->order);
>  		prep_new_huge_page(h, page, page_to_nid(page));
>  	}
>  }
> diff --git a/mm/internal.h b/mm/internal.h
> index 08b8dea..92729ea 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -17,6 +17,7 @@ void free_pgtables(struct mmu_gather *tlb, struct
> vm_area_struct *start_vma, unsigned long floor, unsigned long ceiling);
>
>  extern void prep_compound_page(struct page *page, unsigned long order);
> +extern void prep_compound_gigantic_page(struct page *page, unsigned long
> order);
>
>  static inline void set_page_count(struct page *page, int v)
>  {
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 27b8681..dbeb3f8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -268,14 +268,28 @@ void prep_compound_page(struct page *page, unsigned
> long order) {
>  	int i;
>  	int nr_pages = 1 << order;
> +
> +	set_compound_page_dtor(page, free_compound_page);
> +	set_compound_order(page, order);
> +	__SetPageHead(page);
> +	for (i = 1; i < nr_pages; i++) {
> +		struct page *p = page + i;
> +
> +		__SetPageTail(p);
> +		p->first_page = page;
> +	}
> +}
> +
> +void prep_compound_gigantic_page(struct page *page, unsigned long order)
> +{
> +	int i;
> +	int nr_pages = 1 << order;
>  	struct page *p = page + 1;
>
>  	set_compound_page_dtor(page, free_compound_page);
>  	set_compound_order(page, order);
>  	__SetPageHead(page);
> -	for (i = 1; i < nr_pages; i++, p++) {
> -		if (unlikely((i & (MAX_ORDER_NR_PAGES - 1)) == 0))
> -			p = pfn_to_page(page_to_pfn(page) + i);
> +	for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
>  		__SetPageTail(p);
>  		p->first_page = page;
>  	}
> @@ -285,7 +299,6 @@ static void destroy_compound_page(struct page *page,
> unsigned long order) {
>  	int i;
>  	int nr_pages = 1 << order;
> -	struct page *p = page + 1;
>
>  	if (unlikely(compound_order(page) != order))
>  		bad_page(page);
> @@ -293,9 +306,8 @@ static void destroy_compound_page(struct page *page,
> unsigned long order) if (unlikely(!PageHead(page)))
>  			bad_page(page);
>  	__ClearPageHead(page);
> -	for (i = 1; i < nr_pages; i++, p++) {
> -		if (unlikely((i & (MAX_ORDER_NR_PAGES - 1)) == 0))
> -			p = pfn_to_page(page_to_pfn(page) + i);
> +	for (i = 1; i < nr_pages; i++) {
> +		struct page *p = page + i;
>
>  		if (unlikely(!PageTail(p) |
>  				(p->first_page != page)))
--
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