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SubjectRe: [PATCH] [12/18] Add support to allocate hugetlb pages that are larger than MAX_ORDER
Andi Kleen 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.

This looks like an off-by-one error here and in the code below -- it
should be ">= MAX_ORDER" not "> MAX_ORDER". Cf alloc_pages() in gfp.h:

if (unlikely(order >= MAX_ORDER))
return NULL;
> 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;
> +
> 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];
> + }
> +
> /*
> * Increase the pool size
> * First take pages out of surplus state. Then make up the

-Andrew Hastings
Cray Inc.


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