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

Hyeonggon Yoo
2022-10-15T04:34:45Z

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@roeck-us.net>
Fixes: d6a71648dbc0 ("mm/slab: kmalloc: pass requests larger than order-1 page to page allocator")
Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
---

@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