Demote page functionality will split a huge page into a number of huge
pages of a smaller size. For example, on x86 a 1GB huge page can be
demoted into 512 2M huge pages. Demotion is done 'in place' by simply
splitting the huge page.
Added '*_for_demote' wrappers for remove_hugetlb_page,
destroy_compound_gigantic_page and prep_compound_gigantic_page for use
by demote code.
Signed-off-by: Mike Kravetz <[email protected]>
---
mm/hugetlb.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 74 insertions(+), 8 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ccbe323c992b..aec2e737d0cd 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1270,7 +1270,7 @@ static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
((node = hstate_next_node_to_free(hs, mask)) || 1); \
nr_nodes--)
-#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
+/* used to demote non-gigantic_huge pages as well */
static void __destroy_compound_gigantic_page(struct page *page,
unsigned int order, bool demote)
{
@@ -1293,6 +1293,13 @@ static void __destroy_compound_gigantic_page(struct page *page,
__ClearPageHead(page);
}
+static void destroy_compound_gigantic_page_for_demote(struct page *page,
+ unsigned int order)
+{
+ __destroy_compound_gigantic_page(page, order, true);
+}
+
+#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
static void destroy_compound_gigantic_page(struct page *page,
unsigned int order)
{
@@ -1438,6 +1445,12 @@ static void remove_hugetlb_page(struct hstate *h, struct page *page,
__remove_hugetlb_page(h, page, adjust_surplus, false);
}
+static void remove_hugetlb_page_for_demote(struct hstate *h, struct page *page,
+ bool adjust_surplus)
+{
+ __remove_hugetlb_page(h, page, adjust_surplus, true);
+}
+
static void add_hugetlb_page(struct hstate *h, struct page *page,
bool adjust_surplus)
{
@@ -1779,6 +1792,12 @@ static bool prep_compound_gigantic_page(struct page *page, unsigned int order)
return __prep_compound_gigantic_page(page, order, false);
}
+static bool prep_compound_gigantic_page_for_demote(struct page *page,
+ unsigned int order)
+{
+ return __prep_compound_gigantic_page(page, order, true);
+}
+
/*
* PageHuge() only returns true for hugetlbfs pages, but not for normal or
* transparent huge pages. See the PageTransHuge() documentation for more
@@ -3302,9 +3321,54 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
return 0;
}
+static int demote_free_huge_page(struct hstate *h, struct page *page)
+{
+ int i, nid = page_to_nid(page);
+ struct hstate *target_hstate;
+ int rc = 0;
+
+ target_hstate = size_to_hstate(PAGE_SIZE << h->demote_order);
+
+ remove_hugetlb_page_for_demote(h, page, false);
+ spin_unlock_irq(&hugetlb_lock);
+
+ rc = alloc_huge_page_vmemmap(h, page);
+ if (rc) {
+ /* Allocation of vmemmmap failed, we can not demote page */
+ spin_lock_irq(&hugetlb_lock);
+ set_page_refcounted(page);
+ add_hugetlb_page(h, page, false);
+ return rc;
+ }
+
+ /*
+ * Use destroy_compound_gigantic_page_for_demote for all huge page
+ * sizes as it will not ref count pages.
+ */
+ destroy_compound_gigantic_page_for_demote(page, huge_page_order(h));
+
+ for (i = 0; i < pages_per_huge_page(h);
+ i += pages_per_huge_page(target_hstate)) {
+ if (hstate_is_gigantic(target_hstate))
+ prep_compound_gigantic_page_for_demote(page + i,
+ target_hstate->order);
+ else
+ prep_compound_page(page + i, target_hstate->order);
+ set_page_private(page + i, 0);
+ set_page_refcounted(page + i);
+ prep_new_huge_page(target_hstate, page + i, nid);
+ put_page(page + i);
+ }
+
+ spin_lock_irq(&hugetlb_lock);
+ return rc;
+}
+
static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
__must_hold(&hugetlb_lock)
{
+ int nr_nodes, node;
+ struct page *page;
int rc = 0;
lockdep_assert_held(&hugetlb_lock);
@@ -3313,9 +3377,15 @@ static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
if (!h->demote_order)
return rc;
- /*
- * TODO - demote fucntionality will be added in subsequent patch
- */
+ for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
+ if (!list_empty(&h->hugepage_freelists[node])) {
+ page = list_entry(h->hugepage_freelists[node].next,
+ struct page, lru);
+ rc = !demote_free_huge_page(h, page);
+ break;
+ }
+ }
+
return rc;
}
@@ -3550,10 +3620,6 @@ static ssize_t demote_store(struct kobject *kobj,
/*
* Check for available pages to demote each time thorough the
* loop as demote_pool_huge_page will drop hugetlb_lock.
- *
- * NOTE: demote_pool_huge_page does not yet drop hugetlb_lock
- * but will when full demote functionality is added in a later
- * patch.
*/
if (nid != NUMA_NO_NODE)
nr_available = h->free_huge_pages_node[nid];
--
2.31.1
On Fri, Oct 01, 2021 at 10:52:10AM -0700, Mike Kravetz wrote:
> Demote page functionality will split a huge page into a number of huge
> pages of a smaller size. For example, on x86 a 1GB huge page can be
> demoted into 512 2M huge pages. Demotion is done 'in place' by simply
> splitting the huge page.
>
> Added '*_for_demote' wrappers for remove_hugetlb_page,
> destroy_compound_gigantic_page and prep_compound_gigantic_page for use
> by demote code.
>
> Signed-off-by: Mike Kravetz <[email protected]>
> ---
> mm/hugetlb.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 74 insertions(+), 8 deletions(-)
>
...
> +static int demote_free_huge_page(struct hstate *h, struct page *page)
> +{
> + int i, nid = page_to_nid(page);
> + struct hstate *target_hstate;
> + int rc = 0;
> +
> + target_hstate = size_to_hstate(PAGE_SIZE << h->demote_order);
> +
> + remove_hugetlb_page_for_demote(h, page, false);
> + spin_unlock_irq(&hugetlb_lock);
> +
> + rc = alloc_huge_page_vmemmap(h, page);
> + if (rc) {
> + /* Allocation of vmemmmap failed, we can not demote page */
> + spin_lock_irq(&hugetlb_lock);
> + set_page_refcounted(page);
> + add_hugetlb_page(h, page, false);
> + return rc;
> + }
Question: You keep the original error code returned from alloc_huge_page_vmemmap()
here, but then you lose it on demote_pool_huge_page() when doing the
!demote_free_huge_page. Would not make more sense to keep it all the way down to
demote_store() in case you want to return the actual error code?
> +
> + /*
> + * Use destroy_compound_gigantic_page_for_demote for all huge page
> + * sizes as it will not ref count pages.
> + */
> + destroy_compound_gigantic_page_for_demote(page, huge_page_order(h));
It seems that for now we only allow gigantic pages to be demoted, but
destroy_compound_gigantic_page_for_demote feels kind of wrong, even
if it is only a wrapper that ends up calling _*gigantic_ functions.
We want a routine that destroy a hugetlb to be demoted into smaller hugetlb
pages, so the name gigantic makes little sense to appear in my opinion.
> static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
> __must_hold(&hugetlb_lock)
> {
> + int nr_nodes, node;
> + struct page *page;
> int rc = 0;
>
> lockdep_assert_held(&hugetlb_lock);
> @@ -3313,9 +3377,15 @@ static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
> if (!h->demote_order)
> return rc;
>
> - /*
> - * TODO - demote fucntionality will be added in subsequent patch
> - */
> + for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
> + if (!list_empty(&h->hugepage_freelists[node])) {
> + page = list_entry(h->hugepage_freelists[node].next,
> + struct page, lru);
> + rc = !demote_free_huge_page(h, page);
I kinda dislike this as I pointed out.
--
Oscar Salvador
SUSE Labs
On 10/6/21 1:41 AM, Oscar Salvador wrote:
> On Fri, Oct 01, 2021 at 10:52:10AM -0700, Mike Kravetz wrote:
>> Demote page functionality will split a huge page into a number of huge
>> pages of a smaller size. For example, on x86 a 1GB huge page can be
>> demoted into 512 2M huge pages. Demotion is done 'in place' by simply
>> splitting the huge page.
>>
>> Added '*_for_demote' wrappers for remove_hugetlb_page,
>> destroy_compound_gigantic_page and prep_compound_gigantic_page for use
>> by demote code.
>>
>> Signed-off-by: Mike Kravetz <[email protected]>
>> ---
>> mm/hugetlb.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++-----
>> 1 file changed, 74 insertions(+), 8 deletions(-)
>>
> ...
>> +static int demote_free_huge_page(struct hstate *h, struct page *page)
>> +{
>> + int i, nid = page_to_nid(page);
>> + struct hstate *target_hstate;
>> + int rc = 0;
>> +
>> + target_hstate = size_to_hstate(PAGE_SIZE << h->demote_order);
>> +
>> + remove_hugetlb_page_for_demote(h, page, false);
>> + spin_unlock_irq(&hugetlb_lock);
>> +
>> + rc = alloc_huge_page_vmemmap(h, page);
>> + if (rc) {
>> + /* Allocation of vmemmmap failed, we can not demote page */
>> + spin_lock_irq(&hugetlb_lock);
>> + set_page_refcounted(page);
>> + add_hugetlb_page(h, page, false);
>> + return rc;
>> + }
>
> Question: You keep the original error code returned from alloc_huge_page_vmemmap()
> here, but then you lose it on demote_pool_huge_page() when doing the
> !demote_free_huge_page. Would not make more sense to keep it all the way down to
> demote_store() in case you want to return the actual error code?
>
Yes, I will return it all the way to demote_store (and the user).
>> +
>> + /*
>> + * Use destroy_compound_gigantic_page_for_demote for all huge page
>> + * sizes as it will not ref count pages.
>> + */
>> + destroy_compound_gigantic_page_for_demote(page, huge_page_order(h));
>
> It seems that for now we only allow gigantic pages to be demoted, but
> destroy_compound_gigantic_page_for_demote feels kind of wrong, even
> if it is only a wrapper that ends up calling _*gigantic_ functions.
>
> We want a routine that destroy a hugetlb to be demoted into smaller hugetlb
> pages, so the name gigantic makes little sense to appear in my opinion.
>
Agree, I do not love the name. Since it is only a wrapper, how about
destroy_hugetlb_page_for_demote? And, change those other *_for_demote
wrappers to similiarly not have gigantic in their names.
>> static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
>> __must_hold(&hugetlb_lock)
>> {
>> + int nr_nodes, node;
>> + struct page *page;
>> int rc = 0;
>>
>> lockdep_assert_held(&hugetlb_lock);
>> @@ -3313,9 +3377,15 @@ static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
>> if (!h->demote_order)
>> return rc;
>>
>> - /*
>> - * TODO - demote fucntionality will be added in subsequent patch
>> - */
>> + for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
>> + if (!list_empty(&h->hugepage_freelists[node])) {
>> + page = list_entry(h->hugepage_freelists[node].next,
>> + struct page, lru);
>> + rc = !demote_free_huge_page(h, page);
>
> I kinda dislike this as I pointed out.
>
Will change.
Thanks for all your comments!
--
Mike Kravetz
On Wed, Oct 06, 2021 at 11:52:33AM -0700, Mike Kravetz wrote:
> Agree, I do not love the name. Since it is only a wrapper, how about
> destroy_hugetlb_page_for_demote? And, change those other *_for_demote
> wrappers to similiarly not have gigantic in their names.
Yes, makes sense to me. We want the names to be generic and not tied to
gigantic stuff.
Thanks Mike
--
Oscar Salvador
SUSE L3