diff mbox series

[v7,6/7] mm: Make alloc_contig_range handle in-use hugetlb pages

Message ID 20210413104747.12177-7-osalvador@suse.de (mailing list archive)
State New
Headers show
Series Make alloc_contig_range handle Hugetlb pages | expand

Commit Message

Oscar Salvador April 13, 2021, 10:47 a.m. UTC
alloc_contig_range() will fail if it finds a HugeTLB page within the range,
without a chance to handle them. Since HugeTLB pages can be migrated as any
LRU or Movable page, it does not make sense to bail out without trying.
Enable the interface to recognize in-use HugeTLB pages so we can migrate
them, and have much better chances to succeed the call.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 include/linux/hugetlb.h |  5 +++--
 mm/compaction.c         | 12 +++++++++++-
 mm/hugetlb.c            | 22 +++++++++++++++++-----
 mm/vmscan.c             |  5 +++--
 4 files changed, 34 insertions(+), 10 deletions(-)

Comments

Mike Kravetz April 13, 2021, 10:48 p.m. UTC | #1
On 4/13/21 3:47 AM, Oscar Salvador wrote:
> alloc_contig_range() will fail if it finds a HugeTLB page within the range,
> without a chance to handle them. Since HugeTLB pages can be migrated as any
> LRU or Movable page, it does not make sense to bail out without trying.
> Enable the interface to recognize in-use HugeTLB pages so we can migrate
> them, and have much better chances to succeed the call.
> 
> Signed-off-by: Oscar Salvador <osalvador@suse.de>
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
> Acked-by: Michal Hocko <mhocko@suse.com>

One small issue/question/request below.

> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 4a664d6e82c1..24a453ff47f2 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2270,10 +2270,12 @@ static void restore_reserve_on_error(struct hstate *h,
>   * alloc_and_dissolve_huge_page - Allocate a new page and dissolve the old one
>   * @h: struct hstate old page belongs to
>   * @old_page: Old page to dissolve
> + * @list: List to isolate the page in case we need to
>   * Returns 0 on success, otherwise negated error.
>   */
>  
> -static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page)
> +static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
> +					struct list_head *list)
>  {
>  	gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
>  	int nid = page_to_nid(old_page);
> @@ -2300,9 +2302,13 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page)
>  		goto free_new;
>  	} else if (page_count(old_page)) {
>  		/*
> -		 * Someone has grabbed the page, fail for now.
> +		 * Someone has grabbed the page, try to isolate it here.
> +		 * Fail with -EBUSY if not possible.
>  		 */
> -		ret = -EBUSY;
> +		spin_unlock_irq(&hugetlb_lock);
> +		if (!isolate_huge_page(old_page, list))
> +			ret = -EBUSY;
> +		spin_lock_irq(&hugetlb_lock);
>  		goto free_new;

The label free_new is:

free_new:
        spin_unlock_irq(&hugetlb_lock);
        __free_pages(new_page, huge_page_order(h));

        return ret;

So, we are locking and immediately unlocking without any code in
between.  Usually, I don't like like multiple labels before return.
However, perhaps we should add another to avoid this unnecessary
cycle.  On the other hand, this is an uncommon race condition so the
simple code may be acceptable.
Oscar Salvador April 14, 2021, 4:52 a.m. UTC | #2
On Tue, Apr 13, 2021 at 03:48:53PM -0700, Mike Kravetz wrote:
> The label free_new is:
> 
> free_new:
>         spin_unlock_irq(&hugetlb_lock);
>         __free_pages(new_page, huge_page_order(h));
> 
>         return ret;
> 
> So, we are locking and immediately unlocking without any code in
> between.  Usually, I don't like like multiple labels before return.
> However, perhaps we should add another to avoid this unnecessary
> cycle.  On the other hand, this is an uncommon race condition so the
> simple code may be acceptable.

I guess we could have something like:

 free_new:
         spin_unlock_irq(&hugetlb_lock);
 free_new_nolock:
         __free_pages(new_page, huge_page_order(h));
 
         return ret;

And let the retry go to there without locking. But as you said, the
racecondition is rare enough, so I am not sure if this buys us much.
But I can certainly add it if you feel strong about it.
Mike Kravetz April 14, 2021, 5:07 p.m. UTC | #3
On 4/13/21 9:52 PM, Oscar Salvador wrote:
> On Tue, Apr 13, 2021 at 03:48:53PM -0700, Mike Kravetz wrote:
>> The label free_new is:
>>
>> free_new:
>>         spin_unlock_irq(&hugetlb_lock);
>>         __free_pages(new_page, huge_page_order(h));
>>
>>         return ret;
>>
>> So, we are locking and immediately unlocking without any code in
>> between.  Usually, I don't like like multiple labels before return.
>> However, perhaps we should add another to avoid this unnecessary
>> cycle.  On the other hand, this is an uncommon race condition so the
>> simple code may be acceptable.
> 
> I guess we could have something like:
> 
>  free_new:
>          spin_unlock_irq(&hugetlb_lock);
>  free_new_nolock:
>          __free_pages(new_page, huge_page_order(h));
>  
>          return ret;
> 
> And let the retry go to there without locking. But as you said, the
> racecondition is rare enough, so I am not sure if this buys us much.
> But I can certainly add it if you feel strong about it.

No strong feelings.  I am fine with it as is.
diff mbox series

Patch

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index b2d2118bfd1a..b92f25ccef58 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -595,7 +595,7 @@  struct huge_bootmem_page {
 	struct hstate *hstate;
 };
 
-int isolate_or_dissolve_huge_page(struct page *page);
+int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list);
 struct page *alloc_huge_page(struct vm_area_struct *vma,
 				unsigned long addr, int avoid_reserve);
 struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
@@ -878,7 +878,8 @@  static inline void huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
 #else	/* CONFIG_HUGETLB_PAGE */
 struct hstate {};
 
-static inline int isolate_or_dissolve_huge_page(struct page *page)
+static inline int isolate_or_dissolve_huge_page(struct page *page,
+						struct list_head *list)
 {
 	return -ENOMEM;
 }
diff --git a/mm/compaction.c b/mm/compaction.c
index 89426b6d1ea3..bb8ff3543972 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -909,7 +909,7 @@  isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		}
 
 		if (PageHuge(page) && cc->alloc_contig) {
-			ret = isolate_or_dissolve_huge_page(page);
+			ret = isolate_or_dissolve_huge_page(page, &cc->migratepages);
 
 			/*
 			 * Fail isolation in case isolate_or_dissolve_huge_page
@@ -927,6 +927,15 @@  isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 				goto isolate_fail;
 			}
 
+			if (PageHuge(page)) {
+				/*
+				 * Hugepage was successfully isolated and placed
+				 * on the cc->migratepages list.
+				 */
+				low_pfn += compound_nr(page) - 1;
+				goto isolate_success_no_list;
+			}
+
 			/*
 			 * Ok, the hugepage was dissolved. Now these pages are
 			 * Buddy and cannot be re-allocated because they are
@@ -1068,6 +1077,7 @@  isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 
 isolate_success:
 		list_add(&page->lru, &cc->migratepages);
+isolate_success_no_list:
 		cc->nr_migratepages += compound_nr(page);
 		nr_isolated += compound_nr(page);
 
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 4a664d6e82c1..24a453ff47f2 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2270,10 +2270,12 @@  static void restore_reserve_on_error(struct hstate *h,
  * alloc_and_dissolve_huge_page - Allocate a new page and dissolve the old one
  * @h: struct hstate old page belongs to
  * @old_page: Old page to dissolve
+ * @list: List to isolate the page in case we need to
  * Returns 0 on success, otherwise negated error.
  */
 
-static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page)
+static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
+					struct list_head *list)
 {
 	gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
 	int nid = page_to_nid(old_page);
@@ -2300,9 +2302,13 @@  static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page)
 		goto free_new;
 	} else if (page_count(old_page)) {
 		/*
-		 * Someone has grabbed the page, fail for now.
+		 * Someone has grabbed the page, try to isolate it here.
+		 * Fail with -EBUSY if not possible.
 		 */
-		ret = -EBUSY;
+		spin_unlock_irq(&hugetlb_lock);
+		if (!isolate_huge_page(old_page, list))
+			ret = -EBUSY;
+		spin_lock_irq(&hugetlb_lock);
 		goto free_new;
 	} else if (!HPageFreed(old_page)) {
 		/*
@@ -2350,10 +2356,11 @@  static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page)
 	return ret;
 }
 
-int isolate_or_dissolve_huge_page(struct page *page)
+int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list)
 {
 	struct hstate *h;
 	struct page *head;
+	int ret = -EBUSY;
 
 	/*
 	 * The page might have been dissolved from under our feet, so make sure
@@ -2378,7 +2385,12 @@  int isolate_or_dissolve_huge_page(struct page *page)
 	if (hstate_is_gigantic(h))
 		return -ENOMEM;
 
-	return alloc_and_dissolve_huge_page(h, head);
+	if (page_count(head) && isolate_huge_page(head, list))
+		ret = 0;
+	else if (!page_count(head))
+		ret = alloc_and_dissolve_huge_page(h, head, list);
+
+	return ret;
 }
 
 struct page *alloc_huge_page(struct vm_area_struct *vma,
diff --git a/mm/vmscan.c b/mm/vmscan.c
index bb8321026c0c..5199b9696bab 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1703,8 +1703,9 @@  unsigned int reclaim_clean_pages_from_list(struct zone *zone,
 	LIST_HEAD(clean_pages);
 
 	list_for_each_entry_safe(page, next, page_list, lru) {
-		if (page_is_file_lru(page) && !PageDirty(page) &&
-		    !__PageMovable(page) && !PageUnevictable(page)) {
+		if (!PageHuge(page) && page_is_file_lru(page) &&
+		    !PageDirty(page) && !__PageMovable(page) &&
+		    !PageUnevictable(page)) {
 			ClearPageActive(page);
 			list_move(&page->lru, &clean_pages);
 		}