[PATCH] mm/slab: use kmalloc_node() for off slab freelist_idx_t array allocation

[Hyeonggon Yoo]

After commit d6a71648dbc0 ("mm/slab: kmalloc: pass requests larger than
order-1 page to page allocator"), SLAB passes large ( > PAGE_SIZE * 2)
requests to buddy like SLUB does.

SLAB has been using kmalloc caches to allocate freelist_idx_t array for
off slab caches. But after the commit, freelist_size can be bigger than
KMALLOC_MAX_CACHE_SIZE.

Instead of using pointer to kmalloc cache, use kmalloc_node() and only
check if the kmalloc cache is off slab during calculate_slab_order().
If freelist_size > KMALLOC_MAX_CACHE_SIZE, no looping condition happens
as it allocates freelist_idx_t array directly from buddy.

Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Fixes: d6a71648dbc0 ("mm/slab: kmalloc: pass requests larger than order-1 page to page allocator")
Signed-off-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
---

@Guenter:
	This fixes the issue on my emulation.
	Can you please test this on your environment?

 include/linux/slab_def.h |  1 -
 mm/slab.c                | 37 +++++++++++++++++++------------------
 2 files changed, 19 insertions(+), 19 deletions(-)

diff --git a/include/linux/slab_def.h b/include/linux/slab_def.h
index e24c9aff6fed..f0ffad6a3365 100644
--- a/include/linux/slab_def.h
+++ b/include/linux/slab_def.h
@@ -33,7 +33,6 @@ struct kmem_cache {
 
 	size_t colour;			/* cache colouring range */
 	unsigned int colour_off;	/* colour offset */
-	struct kmem_cache *freelist_cache;
 	unsigned int freelist_size;
 
 	/* constructor func */
diff --git a/mm/slab.c b/mm/slab.c
index a5486ff8362a..d1f6e2c64c2e 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1619,7 +1619,7 @@ static void slab_destroy(struct kmem_cache *cachep, struct slab *slab)
 	 * although actual page can be freed in rcu context
 	 */
 	if (OFF_SLAB(cachep))
-		kmem_cache_free(cachep->freelist_cache, freelist);
+		kfree(freelist);
 }
 
 /*
@@ -1671,21 +1671,27 @@ static size_t calculate_slab_order(struct kmem_cache *cachep,
 		if (flags & CFLGS_OFF_SLAB) {
 			struct kmem_cache *freelist_cache;
 			size_t freelist_size;
+			size_t freelist_cache_size;
 
 			freelist_size = num * sizeof(freelist_idx_t);
-			freelist_cache = kmalloc_slab(freelist_size, 0u);
-			if (!freelist_cache)
-				continue;
-
-			/*
-			 * Needed to avoid possible looping condition
-			 * in cache_grow_begin()
-			 */
-			if (OFF_SLAB(freelist_cache))
-				continue;
+			if (freelist_size > KMALLOC_MAX_CACHE_SIZE) {
+				freelist_cache_size = PAGE_SIZE << get_order(freelist_size);
+			} else {
+				freelist_cache = kmalloc_slab(freelist_size, 0u);
+				if (!freelist_cache)
+					continue;
+				freelist_cache_size = freelist_cache->size;
+
+				/*
+				 * Needed to avoid possible looping condition
+				 * in cache_grow_begin()
+				 */
+				if (OFF_SLAB(freelist_cache))
+					continue;
+			}
 
 			/* check if off slab has enough benefit */
-			if (freelist_cache->size > cachep->size / 2)
+			if (freelist_cache_size > cachep->size / 2)
 				continue;
 		}
 
@@ -2061,11 +2067,6 @@ int __kmem_cache_create(struct kmem_cache *cachep, slab_flags_t flags)
 		cachep->flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER);
 #endif
 
-	if (OFF_SLAB(cachep)) {
-		cachep->freelist_cache =
-			kmalloc_slab(cachep->freelist_size, 0u);
-	}
-
 	err = setup_cpu_cache(cachep, gfp);
 	if (err) {
 		__kmem_cache_release(cachep);
@@ -2292,7 +2293,7 @@ static void *alloc_slabmgmt(struct kmem_cache *cachep,
 		freelist = NULL;
 	else if (OFF_SLAB(cachep)) {
 		/* Slab management obj is off-slab. */
-		freelist = kmem_cache_alloc_node(cachep->freelist_cache,
+		freelist = kmalloc_node(cachep->freelist_size,
 					      local_flags, nodeid);
 	} else {
 		/* We will use last bytes at the slab for freelist */
-- 
2.32.0