Re: [PATCH v4 4/7] mm: page_owner: add support for splitting to any order in split page_owner.

[David Hildenbrand]

On 13.02.24 22:55, Zi Yan wrote:
From: Zi Yan <z...@nvidia.com>
It adds a new_order parameter to set new page order in page owner.
It prepares for upcoming changes to support split huge page to any
lower order.

Signed-off-by: Zi Yan <z...@nvidia.com>
---
  include/linux/page_owner.h | 10 +++++-----
  mm/huge_memory.c           |  2 +-
  mm/page_alloc.c            |  4 ++--
  mm/page_owner.c            |  9 +++++----
  4 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/include/linux/page_owner.h b/include/linux/page_owner.h
index d7878523adfc..a784ba69f67f 100644
--- a/include/linux/page_owner.h
+++ b/include/linux/page_owner.h
@@ -11,7 +11,7 @@ extern struct page_ext_operations page_owner_ops;
  extern void __reset_page_owner(struct page *page, unsigned short order);
  extern void __set_page_owner(struct page *page,
                        unsigned short order, gfp_t gfp_mask);
-extern void __split_page_owner(struct page *page, int order);
+extern void __split_page_owner(struct page *page, int old_order, int 
new_order);
  extern void __folio_copy_owner(struct folio *newfolio, struct folio *old);
  extern void __set_page_owner_migrate_reason(struct page *page, int reason);
  extern void __dump_page_owner(const struct page *page);
@@ -31,10 +31,10 @@ static inline void set_page_owner(struct page *page,
                __set_page_owner(page, order, gfp_mask);
  }
  
-static inline void split_page_owner(struct page *page, int order)
+static inline void split_page_owner(struct page *page, int old_order, int 
new_order)
  {
        if (static_branch_unlikely(&page_owner_inited))
-               __split_page_owner(page, order);
+               __split_page_owner(page, old_order, new_order);
  }
  static inline void folio_copy_owner(struct folio *newfolio, struct folio *old)
  {
@@ -56,11 +56,11 @@ static inline void reset_page_owner(struct page *page, 
unsigned short order)
  {
  }
  static inline void set_page_owner(struct page *page,
-                       unsigned int order, gfp_t gfp_mask)
+                       unsigned short order, gfp_t gfp_mask)
  {
  }
  static inline void split_page_owner(struct page *page,
-                       int order)
+                       int old_order, int new_order)
  {
  }
  static inline void folio_copy_owner(struct folio *newfolio, struct folio 
*folio)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 3d30eccd3a7f..ad7133c97428 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2919,7 +2919,7 @@ static void __split_huge_page(struct page *page, struct 
list_head *list,
        unlock_page_lruvec(lruvec);
        /* Caller disabled irqs, so they are still disabled here */
  
-	split_page_owner(head, order);
+       split_page_owner(head, order, 0);
  
  	/* See comment in __split_huge_page_tail() */
        if (PageAnon(head)) {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9d4dd41d0647..e0f107b21c98 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2652,7 +2652,7 @@ void split_page(struct page *page, unsigned int order)
  
  	for (i = 1; i < (1 << order); i++)
                set_page_refcounted(page + i);
-       split_page_owner(page, order);
+       split_page_owner(page, order, 0);
        split_page_memcg(page, order, 0);
  }
  EXPORT_SYMBOL_GPL(split_page);
@@ -4837,7 +4837,7 @@ static void *make_alloc_exact(unsigned long addr, 
unsigned int order,
                struct page *page = virt_to_page((void *)addr);
                struct page *last = page + nr;
  
-		split_page_owner(page, order);
+               split_page_owner(page, order, 0);
                split_page_memcg(page, order, 0);
                while (page < --last)
                        set_page_refcounted(last);
diff --git a/mm/page_owner.c b/mm/page_owner.c
index 1319e402c2cf..ebbffa0501db 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -292,19 +292,20 @@ void __set_page_owner_migrate_reason(struct page *page, 
int reason)
        page_ext_put(page_ext);
  }
  
-void __split_page_owner(struct page *page, int order)
+void __split_page_owner(struct page *page, int old_order, int new_order)
  {
        int i;
        struct page_ext *page_ext = page_ext_get(page);
        struct page_owner *page_owner;
-       unsigned int nr = 1 << order;
+       unsigned int old_nr = 1 << old_order;
+       unsigned int new_nr = 1 << new_order;
  
  	if (unlikely(!page_ext))
                return;
  
-	for (i = 0; i < nr; i++) {
+       for (i = 0; i < old_nr; i += new_nr) {
                page_owner = get_page_owner(page_ext);
-               page_owner->order = 0;
+               page_owner->order = new_order;
                page_ext = page_ext_next(page_ext);

Staring at __set_page_owner_handle(), we do set all 1<<order page_exts 
(corresponding to 1<<order "struct page"s) to have ->order set.

Wouldn't you have to do the same here?

for (i = 0; i < 1 << old_order; i++) {
        page_owner = get_page_owner(page_ext);
        page_owner->order = new_order;
        page_ext = page_ext_next(page_ext);
}

--
Cheers,

David / dhildenb