linux-kernel - [PATCH v2 2/2] mm, slab: use frozen pages for large kmalloc

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Message-Id: <20250602-frozen-pages-for-large-kmalloc-v2-2-84a21f2c3640@suse.cz>
Date: Mon, 02 Jun 2025 13:02:13 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Christoph Lameter <cl@...ux.com>, David Rientjes <rientjes@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
 Roman Gushchin <roman.gushchin@...ux.dev>, Harry Yoo <harry.yoo@...cle.com>, 
 Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org, 
 linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH v2 2/2] mm, slab: use frozen pages for large kmalloc

Since slab pages are now frozen, it makes sense to have large kmalloc()
objects behave same as small kmalloc(), as the choice between the two is
an implementation detail depending on allocation size.

Notably, increasing refcount on a slab page containing kmalloc() object
is not possible anymore, so it should be consistent for large kmalloc
pages.

Therefore, change large kmalloc to use the frozen pages API.

Because of some unexpected fallout in the slab pages case (see commit
b9c0e49abfca ("mm: decline to manipulate the refcount on a slab page"),
implement the same kind of checks and warnings as part of this change.

Notably, networking code using sendpage_ok() to determine whether the
page refcount can be manipulated in the network stack should continue
behaving correctly. Before this change, the function returns true for
large kmalloc pages and page refcount can be manipulated. After this
change, the function will return false.

Acked-by: Roman Gushchin <roman.gushchin@...ux.dev>
Acked-by: Harry Yoo <harry.yoo@...cle.com>
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 include/linux/mm.h | 4 +++-
 mm/slub.c          | 6 +++---
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index bf55206935c467f7508e863332063bb15f904a24..d3eb6adf9fa949fbd611470182a03c743b16aac7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1549,6 +1549,8 @@ static inline void get_page(struct page *page)
 	struct folio *folio = page_folio(page);
 	if (WARN_ON_ONCE(folio_test_slab(folio)))
 		return;
+	if (WARN_ON_ONCE(folio_test_large_kmalloc(folio)))
+		return;
 	folio_get(folio);
 }
 
@@ -1643,7 +1645,7 @@ static inline void put_page(struct page *page)
 {
 	struct folio *folio = page_folio(page);
 
-	if (folio_test_slab(folio))
+	if (folio_test_slab(folio) || folio_test_large_kmalloc(folio))
 		return;
 
 	folio_put(folio);
diff --git a/mm/slub.c b/mm/slub.c
index 11356c701f9f857a2e8cf40bf963ac3abdb5e010..d87015fad2df65629050d9bcd224facd3d2f4033 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4284,9 +4284,9 @@ static void *___kmalloc_large_node(size_t size, gfp_t flags, int node)
 	flags |= __GFP_COMP;
 
 	if (node == NUMA_NO_NODE)
-		folio = (struct folio *)alloc_pages_noprof(flags, order);
+		folio = (struct folio *)alloc_frozen_pages_noprof(flags, order);
 	else
-		folio = (struct folio *)__alloc_pages_noprof(flags, order, node, NULL);
+		folio = (struct folio *)__alloc_frozen_pages_noprof(flags, order, node, NULL);
 
 	if (folio) {
 		ptr = folio_address(folio);
@@ -4783,7 +4783,7 @@ static void free_large_kmalloc(struct folio *folio, void *object)
 	lruvec_stat_mod_folio(folio, NR_SLAB_UNRECLAIMABLE_B,
 			      -(PAGE_SIZE << order));
 	__folio_clear_large_kmalloc(folio);
-	folio_put(folio);
+	free_frozen_pages(&folio->page, order);
 }
 
 /*

-- 
2.49.0