Date: Tue, 18 Mar 2008 16:27:14 +0000
From: Mel Gorman <mel@csn.ul.ie>
To: Andi Kleen <andi@firstfloor.org>
Cc: linux-kernel@vger.kernel.org, pj@sgi.com, linux-mm@kvack.org,
       nickpiggin@yahoo.com.au
Subject: Re: [PATCH] [12/18] Add support to allocate hugetlb pages that are larger than MAX_ORDER
Message-ID: <20080318162714.GL23866@csn.ul.ie>
References: <20080317258.659191058@firstfloor.org> <20080317015826.110AA1B41E0@basil.firstfloor.org>
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On (17/03/08 02:58), Andi Kleen didst pronounce:
> 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>
> 
> ---
>  mm/hugetlb.c |   64 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 62 insertions(+), 2 deletions(-)
> 
> Index: linux/mm/hugetlb.c
> ===================================================================
> --- linux.orig/mm/hugetlb.c
> +++ linux/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>
> @@ -153,7 +154,7 @@ 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) {
>  		update_and_free_page(h, page);
>  		h->surplus_huge_pages--;
>  		h->surplus_huge_pages_node[nid]--;
> @@ -215,6 +216,9 @@ static struct page *alloc_fresh_huge_pag
>  {
>  	struct page *page;
>  
> +	if (h->order > MAX_ORDER)
> +		return NULL;
> +

Should this print out a KERN_INFO message to the effect that pages of
that size must be reserved at boot-time?

>  	page = alloc_pages_node(nid,
>  		htlb_alloc_mask|__GFP_COMP|__GFP_THISNODE|__GFP_NOWARN,
>  			huge_page_order(h));
> @@ -271,6 +275,9 @@ static struct page *alloc_buddy_huge_pag
>  	struct page *page;
>  	unsigned int nid;
>  
> +	if (h->order > MAX_ORDER)
> +		return NULL;
> +
>  	/*
>  	 * Assume we will successfully allocate the surplus page to
>  	 * prevent racing processes from causing the surplus to exceed
> @@ -422,6 +429,10 @@ return_unused_surplus_pages(struct hstat
>  	/* Uncommit the reservation */
>  	h->resv_huge_pages -= unused_resv_pages;
>  
> +	/* Cannot return gigantic pages currently */
> +	if (h->order > MAX_ORDER)
> +		return;
> +
>  	nr_pages = min(unused_resv_pages, h->surplus_huge_pages);
>  
>  	while (nr_pages) {
> @@ -499,6 +510,44 @@ static struct page *alloc_huge_page(stru
>  	return page;
>  }
>  
> +static __initdata LIST_HEAD(huge_boot_pages);
> +
> +struct huge_bm_page {
> +	struct list_head list;
> +	struct hstate *hstate;
> +};
> +
> +static int __init alloc_bm_huge_page(struct hstate *h)
> +{
> +	struct huge_bm_page *m;
> +	m = __alloc_bootmem_node_nopanic(NODE_DATA(h->hugetlb_next_nid),
> +					huge_page_size(h), huge_page_size(h),
> +					0);
> +	if (!m)
> +		return 0;
> +	BUG_ON((unsigned long)virt_to_phys(m) & (huge_page_size(h) - 1));
> +	/* Put them into a private list first because mem_map is not up yet */
> +	list_add(&m->list, &huge_boot_pages);
> +	m->hstate = h;
> +	huge_next_node(h);
> +	return 1;
> +}
> +
> +/* Put bootmem huge pages into the standard lists after mem_map is up */
> +static int __init huge_init_bm(void)
> +{
> +	struct huge_bm_page *m;
> +	list_for_each_entry (m, &huge_boot_pages, list) {
> +		struct page *page = virt_to_page(m);
> +		struct hstate *h = m->hstate;
> +		__ClearPageReserved(page);
> +		prep_compound_page(page, h->order);
> +		huge_new_page(h, page);
> +	}
> +	return 0;
> +}
> +__initcall(huge_init_bm);
> +
>  static int __init hugetlb_init_hstate(struct hstate *h)
>  {
>  	unsigned long i;
> @@ -509,7 +558,10 @@ static int __init hugetlb_init_hstate(st
>  	h->hugetlb_next_nid = first_node(node_online_map);
>  
>  	for (i = 0; i < max_huge_pages[h - hstates]; ++i) {
> -		if (!alloc_fresh_huge_page(h))
> +		if (h->order > MAX_ORDER) {
> +			if (!alloc_bm_huge_page(h))
> +				break;
> +		} else if (!alloc_fresh_huge_page(h))
>  			break;
>  	}
>  	max_huge_pages[h - hstates] = h->free_huge_pages = h->nr_huge_pages = i;
> @@ -581,6 +633,9 @@ static void do_try_to_free_low(struct hs
>  {
>  	int i;
>  
> +	if (h->order > MAX_ORDER)
> +		return;
> +
>  	for (i = 0; i < MAX_NUMNODES; ++i) {
>  		struct page *page, *next;
>  		struct list_head *freel = &h->hugepage_freelists[i];
> @@ -618,6 +673,11 @@ set_max_huge_pages(struct hstate *h, uns
>  
>  	*err = 0;
>  
> +	if (h->order > MAX_ORDER) {
> +		*err = -EINVAL;
> +		return max_huge_pages[h - hstates];
> +	}
> +

Ah, scratch the comment on an earlier patch where I said I cannot see
where err ever gets updated in set_max_huge_pages().

>  	/*
>  	 * Increase the pool size
>  	 * First take pages out of surplus state.  Then make up the
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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