[PATCH 5/6] slab: Allocate frozen pages

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

Since slab does not use the page refcount, it can allocate and
free frozen pages, saving one atomic operation per free.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 mm/slab.c | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index f8cd00f4ba13..c5c53ed304d1 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1355,23 +1355,23 @@ slab_out_of_memory(struct kmem_cache *cachep, gfp_t gfpflags, int nodeid)
 static struct slab *kmem_getpages(struct kmem_cache *cachep, gfp_t flags,
 								int nodeid)
 {
-	struct folio *folio;
+	struct page *page;
 	struct slab *slab;
 
 	flags |= cachep->allocflags;
 
-	folio = (struct folio *) __alloc_pages_node(nodeid, flags, cachep->gfporder);
-	if (!folio) {
+	page = __alloc_frozen_pages(flags, cachep->gfporder, nodeid, NULL);
+	if (!page) {
 		slab_out_of_memory(cachep, flags, nodeid);
 		return NULL;
 	}
 
-	slab = folio_slab(folio);
+	__SetPageSlab(page);
+	slab = (struct slab *)page;
 
 	account_slab(slab, cachep->gfporder, cachep, flags);
-	__folio_set_slab(folio);
 	/* Record if ALLOC_NO_WATERMARKS was set when allocating the slab */
-	if (sk_memalloc_socks() && page_is_pfmemalloc(folio_page(folio, 0)))
+	if (sk_memalloc_socks() && page_is_pfmemalloc(page))
 		slab_set_pfmemalloc(slab);
 
 	return slab;
@@ -1383,18 +1383,17 @@ static struct slab *kmem_getpages(struct kmem_cache *cachep, gfp_t flags,
 static void kmem_freepages(struct kmem_cache *cachep, struct slab *slab)
 {
 	int order = cachep->gfporder;
-	struct folio *folio = slab_folio(slab);
+	struct page *page = (struct page *)slab;
 
-	BUG_ON(!folio_test_slab(folio));
 	__slab_clear_pfmemalloc(slab);
-	__folio_clear_slab(folio);
-	page_mapcount_reset(folio_page(folio, 0));
-	folio->mapping = NULL;
+	__ClearPageSlab(page);
+	page_mapcount_reset(page);
+	page->mapping = NULL;
 
 	if (current->reclaim_state)
 		current->reclaim_state->reclaimed_slab += 1 << order;
 	unaccount_slab(slab, order, cachep);
-	__free_pages(folio_page(folio, 0), order);
+	free_frozen_pages(page, order);
 }
 
 static void kmem_rcu_free(struct rcu_head *head)
-- 
2.34.1