[PATCH v6 05/15] mm/khugepaged: make allocation semantics context-specific

["Zach O'Keefe" <zokeefe@xxxxxxxxxx>]

Add a gfp_t flags member to struct collapse_control that allows contexts
to specify their own allocation semantics.  This decouples the
allocation semantics from
/sys/kernel/mm/transparent_hugepage/khugepaged/defrag.

khugepaged updates this member for every hugepage processed, since the
sysfs setting might change at any time.

Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
---
 mm/khugepaged.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 38488d114073..ba722347bebd 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -92,6 +92,9 @@ struct collapse_control {
 
 	/* Last target selected in khugepaged_find_target_node() */
 	int last_target_node;
+
+	/* gfp used for allocation and memcg charging */
+	gfp_t gfp;
 };
 
 /**
@@ -994,15 +997,14 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 	return true;
 }
 
-static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
+static int alloc_charge_hpage(struct mm_struct *mm, struct page **hpage,
 			      struct collapse_control *cc)
 {
-	gfp_t gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
 	int node = khugepaged_find_target_node(cc);
 
-	if (!khugepaged_alloc_page(hpage, gfp, node))
+	if (!khugepaged_alloc_page(hpage, cc->gfp, node))
 		return SCAN_ALLOC_HUGE_PAGE_FAIL;
-	if (unlikely(mem_cgroup_charge(page_folio(*hpage), mm, gfp)))
+	if (unlikely(mem_cgroup_charge(page_folio(*hpage), mm, cc->gfp)))
 		return SCAN_CGROUP_CHARGE_FAIL;
 	count_memcg_page_event(*hpage, THP_COLLAPSE_ALLOC);
 	return SCAN_SUCCEED;
@@ -1032,7 +1034,7 @@ static void collapse_huge_page(struct mm_struct *mm, unsigned long address,
 	 */
 	mmap_read_unlock(mm);
 
-	result = alloc_charge_hpage(hpage, mm, cc);
+	result = alloc_charge_hpage(mm, hpage, cc);
 	if (result != SCAN_SUCCEED)
 		goto out_nolock;
 
@@ -1613,7 +1615,7 @@ static void collapse_file(struct mm_struct *mm, struct file *file,
 	VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
 	VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
 
-	result = alloc_charge_hpage(hpage, mm, cc);
+	result = alloc_charge_hpage(mm, hpage, cc);
 	if (result != SCAN_SUCCEED)
 		goto out;
 
@@ -2037,8 +2039,7 @@ static void khugepaged_scan_file(struct mm_struct *mm, struct file *file,
 }
 #else
 static void khugepaged_scan_file(struct mm_struct *mm, struct file *file,
-				 pgoff_t start, struct page **hpage,
-				 struct collapse_control *cc)
+				 pgoff_t start, struct collapse_control *cc)
 {
 	BUILD_BUG();
 }
@@ -2121,6 +2122,9 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
 			if (unlikely(khugepaged_test_exit(mm)))
 				goto breakouterloop;
 
+			/* reset gfp flags since sysfs settings might change */
+			cc->gfp = alloc_hugepage_khugepaged_gfpmask() |
+					__GFP_THISNODE;
 			VM_BUG_ON(khugepaged_scan.address < hstart ||
 				  khugepaged_scan.address + HPAGE_PMD_SIZE >
 				  hend);
@@ -2255,6 +2259,7 @@ static int khugepaged(void *none)
 	struct mm_slot *mm_slot;
 	struct collapse_control cc = {
 		.last_target_node = NUMA_NO_NODE,
+		/* .gfp set later  */
 	};
 
 	set_freezable();
-- 
2.36.1.255.ge46751e96f-goog