mm: mmu_gather: prepare to gather encoded page pointers with flags

This is purely a preparatory patch that makes all the data structures
ready for encoding flags with the mmu_gather page pointers.

The code currently always sets the flag to zero and doesn't use it yet,
but now it's tracking the type state along.  The next step will be to
actually start using it.

Link: https://lkml.kernel.org/r/20221109203051.1835763-3-torvalds@linux-foundation.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/s390/include/asm/tlb.h

@@ -25,7 +25,8 @@
 void __tlb_remove_table(void *_table);
 static inline void tlb_flush(struct mmu_gather *tlb);
 static inline bool __tlb_remove_page_size(struct mmu_gather *tlb,
-					  struct page *page, int page_size);
+					  struct encoded_page *page,
+					  int page_size);
 
 #define tlb_flush tlb_flush
 #define pte_free_tlb pte_free_tlb
@@ -42,9 +43,10 @@ static inline bool __tlb_remove_page_size(struct mmu_gather *tlb,
  * has already been freed, so just do free_page_and_swap_cache.
  */
 static inline bool __tlb_remove_page_size(struct mmu_gather *tlb,
-					  struct page *page, int page_size)
+					  struct encoded_page *page,
+					  int page_size)
 {
-	free_page_and_swap_cache(page);
+	free_page_and_swap_cache(encoded_page_ptr(page));
 	return false;
 }
 

include/asm-generic/tlb.h

@@ -246,7 +246,7 @@ struct mmu_gather_batch {
 	struct mmu_gather_batch	*next;
 	unsigned int		nr;
 	unsigned int		max;
-	struct page		*pages[];
+	struct encoded_page	*encoded_pages[];
 };
 
 #define MAX_GATHER_BATCH	\
@@ -260,7 +260,8 @@ struct mmu_gather_batch {
  */
 #define MAX_GATHER_BATCH_COUNT	(10000UL/MAX_GATHER_BATCH)
 
-extern bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page,
+extern bool __tlb_remove_page_size(struct mmu_gather *tlb,
+				   struct encoded_page *page,
 				   int page_size);
 #endif
 
@@ -435,13 +436,13 @@ static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
 static inline void tlb_remove_page_size(struct mmu_gather *tlb,
 					struct page *page, int page_size)
 {
-	if (__tlb_remove_page_size(tlb, page, page_size))
+	if (__tlb_remove_page_size(tlb, encode_page(page, 0), page_size))
 		tlb_flush_mmu(tlb);
 }
 
 static inline bool __tlb_remove_page(struct mmu_gather *tlb, struct page *page)
 {
-	return __tlb_remove_page_size(tlb, page, PAGE_SIZE);
+	return __tlb_remove_page_size(tlb, encode_page(page, 0), PAGE_SIZE);
 }
 
 /* tlb_remove_page

include/linux/swap.h

@@ -463,7 +463,7 @@ static inline unsigned long total_swapcache_pages(void)
 
 extern void free_swap_cache(struct page *page);
 extern void free_page_and_swap_cache(struct page *);
-extern void free_pages_and_swap_cache(struct page **, int);
+extern void free_pages_and_swap_cache(struct encoded_page **, int);
 /* linux/mm/swapfile.c */
 extern atomic_long_t nr_swap_pages;
 extern long total_swap_pages;

mm/mmu_gather.c

@@ -48,7 +48,7 @@ static void tlb_batch_pages_flush(struct mmu_gather *tlb)
 	struct mmu_gather_batch *batch;
 
 	for (batch = &tlb->local; batch && batch->nr; batch = batch->next) {
-		struct page **pages = batch->pages;
+		struct encoded_page **pages = batch->encoded_pages;
 
 		do {
 			/*
@@ -77,7 +77,7 @@ static void tlb_batch_list_free(struct mmu_gather *tlb)
 	tlb->local.next = NULL;
 }
 
-bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, int page_size)
+bool __tlb_remove_page_size(struct mmu_gather *tlb, struct encoded_page *page, int page_size)
 {
 	struct mmu_gather_batch *batch;
 
@@ -92,13 +92,13 @@ bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, int page_
 	 * Add the page and check if we are full. If so
 	 * force a flush.
 	 */
-	batch->pages[batch->nr++] = page;
+	batch->encoded_pages[batch->nr++] = page;
 	if (batch->nr == batch->max) {
 		if (!tlb_next_batch(tlb))
 			return true;
 		batch = tlb->active;
 	}
-	VM_BUG_ON_PAGE(batch->nr > batch->max, page);
+	VM_BUG_ON_PAGE(batch->nr > batch->max, encoded_page_ptr(page));
 
 	return false;
 }

mm/swap_state.c

@@ -303,15 +303,12 @@ void free_page_and_swap_cache(struct page *page)
  * Passed an array of pages, drop them all from swapcache and then release
  * them.  They are removed from the LRU and freed if this is their last use.
  */
-void free_pages_and_swap_cache(struct page **pages, int nr)
+void free_pages_and_swap_cache(struct encoded_page **pages, int nr)
 {
-	struct page **pagep = pages;
-	int i;
-
 	lru_add_drain();
-	for (i = 0; i < nr; i++)
-		free_swap_cache(pagep[i]);
-	release_pages(pagep, nr);
+	for (int i = 0; i < nr; i++)
+		free_swap_cache(encoded_page_ptr(pages[i]));
+	release_pages(pages, nr);
 }
 
 static inline bool swap_use_vma_readahead(void)