[RFC PATCH 8/8] hugetlb: track hugetlb pages allocated via cma_alloc

[Mike Kravetz]

When a hugetlb page allocated via cma_alloc is freed via cma_release
the cma_release call may sleep.  For now, only gigantic pages can be
allocated via cma_alloc.  The routine free_huge_page can not sleep,
so it defers freeing of all gigantic pages to a workqueue.

Use a new hugetlb page specific flag HPageCma to indicate the page was
allocated via cma_alloc.  This flag can be used so that only gigantic
pages allocated via cma_alloc will have deferred freeing.

Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
 include/linux/hugetlb.h |  7 +++++++
 mm/hugetlb.c            | 18 ++++++++++--------
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index a81ca39c06be..0aba6957a73a 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -498,12 +498,18 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
  *	modifications require hugetlb_lock.
  * HPG_freed - Set when page is on the free lists.
  *	Synchronization: hugetlb_lock held for examination and modification.
+ * HPG_cma - Set if huge page was directly allocated from CMA area via
+ *      cma_alloc.  Initially set for gigantic page cma allocations, but can
+ *      be set in non-gigantic pages if gigantic pages are demoted.
+ *	Synchronization: Only accessed or modified when there is only one
+ *	reference to the page at allocation or free time.
  */
 enum hugetlb_page_flags {
 	HPG_restore_reserve = 0,
 	HPG_migratable,
 	HPG_temporary,
 	HPG_freed,
+	HPG_cma,
 	__NR_HPAGEFLAGS,
 };
 
@@ -549,6 +555,7 @@ HPAGEFLAG(RestoreReserve, restore_reserve)
 HPAGEFLAG(Migratable, migratable)
 HPAGEFLAG(Temporary, temporary)
 HPAGEFLAG(Freed, freed)
+HPAGEFLAG(Cma, cma)
 
 #ifdef CONFIG_HUGETLB_PAGE
 
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index b8304b290a73..5efff5ce337f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1241,13 +1241,11 @@ static void destroy_compound_gigantic_page(struct page *page,
 
 static void free_gigantic_page(struct page *page, unsigned int order)
 {
-	/*
-	 * If the page isn't allocated using the cma allocator,
-	 * cma_release() returns false.
-	 */
 #ifdef CONFIG_CMA
-	if (cma_release(hugetlb_cma[page_to_nid(page)], page, 1 << order))
+	if (HPageCma(page)) {
+		cma_release(hugetlb_cma[page_to_nid(page)], page, 1 << order);
 		return;
+	}
 #endif
 
 	free_contig_range(page_to_pfn(page), 1 << order);
@@ -1269,8 +1267,10 @@ static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
 		if (hugetlb_cma[nid]) {
 			page = cma_alloc(hugetlb_cma[nid], nr_pages,
 					huge_page_order(h), true);
-			if (page)
+			if (page) {
+				SetHPageCma(page);
 				return page;
+			}
 		}
 
 		if (!(gfp_mask & __GFP_THISNODE)) {
@@ -1280,8 +1280,10 @@ static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
 
 				page = cma_alloc(hugetlb_cma[node], nr_pages,
 						huge_page_order(h), true);
-				if (page)
+				if (page) {
+					SetHPageCma(page);
 					return page;
+				}
 			}
 		}
 	}
@@ -1397,7 +1399,7 @@ static DECLARE_WORK(free_hpage_work, free_hpage_workfn);
 static bool free_page_may_sleep(struct hstate *h, struct page *page)
 {
 	/* freeing gigantic pages in CMA may sleep */
-	if (hstate_is_gigantic(h))
+	if (HPageCma(page))
 		return true;
 
 	return false;
-- 
2.30.2