On Wed, Apr 19, 2023 at 6:34 AM Vernon Yang [off-list ref] wrote:

On Mon, Apr 17, 2023 at 01:50:19PM -0700, Vishal Moola wrote:

quoted

Introduce utility functions setting the foundation for ptdescs. These
will also assist in the splitting out of ptdesc from struct page.

ptdesc_alloc() is defined to allocate new ptdesc pages as compound
pages. This is to standardize ptdescs by allowing for one allocation
and one free function, in contrast to 2 allocation and 2 free functions.

Signed-off-by: Vishal Moola (Oracle) <redacted>
---
 include/asm-generic/tlb.h | 11 ++++++++++
 include/linux/mm.h        | 44 +++++++++++++++++++++++++++++++++++++++
 include/linux/pgtable.h   | 13 ++++++++++++
 3 files changed, 68 insertions(+)

diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index b46617207c93..6bade9e0e799 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h

@@ -481,6 +481,17 @@ static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
      return tlb_remove_page_size(tlb, page, PAGE_SIZE);
 }

+static inline void tlb_remove_ptdesc(struct mmu_gather *tlb, void *pt)
+{
+     tlb_remove_table(tlb, pt);
+}
+
+/* Like tlb_remove_ptdesc, but for page-like page directories. */
+static inline void tlb_remove_page_ptdesc(struct mmu_gather *tlb, struct ptdesc *pt)
+{
+     tlb_remove_page(tlb, ptdesc_page(pt));
+}
+
 static inline void tlb_change_page_size(struct mmu_gather *tlb,
                                                   unsigned int page_size)
 {

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b18848ae7e22..ec3cbe2fa665 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -2744,6 +2744,45 @@ static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long a
 }
 #endif /* CONFIG_MMU */

+static inline struct ptdesc *virt_to_ptdesc(const void *x)
+{
+     return page_ptdesc(virt_to_head_page(x));
+}
+
+static inline void *ptdesc_to_virt(struct ptdesc *pt)
+{
+     return page_to_virt(ptdesc_page(pt));
+}
+
+static inline void *ptdesc_address(struct ptdesc *pt)
+{
+     return folio_address(ptdesc_folio(pt));
+}
+
+static inline bool ptdesc_is_reserved(struct ptdesc *pt)
+{
+     return folio_test_reserved(ptdesc_folio(pt));
+}
+
+static inline struct ptdesc *ptdesc_alloc(gfp_t gfp, unsigned int order)
+{
+     struct page *page = alloc_pages(gfp | __GFP_COMP, order);
+
+     return page_ptdesc(page);
+}
+
+static inline void ptdesc_free(struct ptdesc *pt)
+{
+     struct page *page = ptdesc_page(pt);
+
+     __free_pages(page, compound_order(page));
+}
+
+static inline void ptdesc_clear(void *x)
+{
+     clear_page(x);
+}
+
 #if USE_SPLIT_PTE_PTLOCKS
 #if ALLOC_SPLIT_PTLOCKS
 void __init ptlock_cache_init(void);

@@ -2970,6 +3009,11 @@ static inline void mark_page_reserved(struct page *page)
      adjust_managed_page_count(page, -1);
 }

+static inline void free_reserved_ptdesc(struct ptdesc *pt)
+{
+     free_reserved_page(ptdesc_page(pt));
+}
+
 /*
  * Default method to free all the __init memory into the buddy system.
  * The freed pages will be poisoned with pattern "poison" if it's within

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 7cc6ea057ee9..7cd803aa38eb 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h

@@ -97,6 +97,19 @@ TABLE_MATCH(ptl, ptl);
 #undef TABLE_MATCH
 static_assert(sizeof(struct ptdesc) <= sizeof(struct page));

+#define ptdesc_page(pt)                      (_Generic((pt),                 \
+     const struct ptdesc *:          (const struct page *)(pt),      \
+     struct ptdesc *:                (struct page *)(pt)))
+
+#define ptdesc_folio(pt)             (_Generic((pt),                 \
+     const struct ptdesc *:          (const struct folio *)(pt),     \
+     struct ptdesc *:                (struct folio *)(pt)))
+
+static inline struct ptdesc *page_ptdesc(struct page *page)
+{
+     return (struct ptdesc *)page;
+}

Hi Vishal,

I'm a little curious, why is the page_ptdesc() using inline functions instead of macro?
If this is any magic, please tell me, thank you very much.

No magic here, I was mainly basing it off Matthew's netmem
series. I'm not too clear on when to use macros vs inlines
myself :/.

If there's a benefit to having it be a macro let me
know and I can make that change in v2.