From: Alexei Starovoitov <ast@xxxxxxxxxx>
Same low/high watermarks for every bucket in bpf_mem_cache consume
significant amount of memory. Preallocating 64 elements of PAGE_SIZE
to the free list is not efficient.
Make low/high watermarks and batching value depend on element size.
This change brings significant memory savings.
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
---
kernel/bpf/memalloc.c | 64 ++++++++++++++++++++++++++++++-------------
1 file changed, 45 insertions(+), 19 deletions(-)
diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index a43630371b9f..be8262f5c9ec 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -105,6 +105,7 @@ struct bpf_mem_cache {
atomic_t free_cnt_nmi;
/* flag to refill nmi list too */
bool refill_nmi_list;
+ int low_watermark, high_watermark, batch;
};
struct bpf_mem_caches {
@@ -123,14 +124,6 @@ static struct llist_node notrace *__llist_del_first(struct llist_head *head)
return entry;
}
-#define BATCH 48
-#define LOW_WATERMARK 32
-#define HIGH_WATERMARK 96
-/* Assuming the average number of elements per bucket is 64, when all buckets
- * are used the total memory will be: 64*16*32 + 64*32*32 + 64*64*32 + ... +
- * 64*4096*32 ~ 20Mbyte
- */
-
/* extra macro useful for testing by randomizing in_nmi condition */
#define bpf_in_nmi() in_nmi()
@@ -238,7 +231,7 @@ static void free_bulk(struct bpf_mem_cache *c)
if (IS_ENABLED(CONFIG_PREEMPT_RT))
local_irq_restore(flags);
free_one(c, llnode);
- } while (cnt > (HIGH_WATERMARK + LOW_WATERMARK) / 2);
+ } while (cnt > (c->high_watermark + c->low_watermark) / 2);
}
static void free_bulk_nmi(struct bpf_mem_cache *c)
@@ -253,7 +246,7 @@ static void free_bulk_nmi(struct bpf_mem_cache *c)
else
cnt = 0;
free_one(c, llnode);
- } while (cnt > (HIGH_WATERMARK + LOW_WATERMARK) / 2);
+ } while (cnt > (c->high_watermark + c->low_watermark) / 2);
}
static void bpf_mem_refill(struct irq_work *work)
@@ -262,12 +255,12 @@ static void bpf_mem_refill(struct irq_work *work)
int cnt;
cnt = c->free_cnt;
- if (cnt < LOW_WATERMARK)
+ if (cnt < c->low_watermark)
/* irq_work runs on this cpu and kmalloc will allocate
* from the current numa node which is what we want here.
*/
- alloc_bulk(c, BATCH, NUMA_NO_NODE);
- else if (cnt > HIGH_WATERMARK)
+ alloc_bulk(c, c->batch, NUMA_NO_NODE);
+ else if (cnt > c->high_watermark)
free_bulk(c);
if (!c->refill_nmi_list)
@@ -276,9 +269,9 @@ static void bpf_mem_refill(struct irq_work *work)
*/
return;
cnt = atomic_read(&c->free_cnt_nmi);
- if (cnt < LOW_WATERMARK)
- alloc_bulk_nmi(c, BATCH, NUMA_NO_NODE);
- else if (cnt > HIGH_WATERMARK)
+ if (cnt < c->low_watermark)
+ alloc_bulk_nmi(c, c->batch, NUMA_NO_NODE);
+ else if (cnt > c->high_watermark)
free_bulk_nmi(c);
c->refill_nmi_list = false;
}
@@ -294,14 +287,47 @@ static void notrace irq_work_raise(struct bpf_mem_cache *c, bool in_nmi)
irq_work_queue(&c->refill_work);
}
+/* For typical bpf map case that uses bpf_mem_cache_alloc and single bucket
+ * the freelist cache will be elem_size * 64 (or less) on each cpu.
+ *
+ * For bpf programs that don't have statically known allocation sizes and
+ * assuming (low_mark + high_mark) / 2 as an average number of elements per
+ * bucket and all buckets are used the total amount of memory in freelists
+ * on each cpu will be:
+ * 64*16 + 64*32 + 64*64 + 64*96 + 64*128 + 64*196 + 64*256 + 32*512 + 16*1024 + 8*2048 + 4*4096
+ * + nmi's reserves
+ * 1*16 + 1*32 + 1*64 + 1*96 + 1*128 + 1*196 + 1*256 + 1*512 + 1*1024 + 1*2048 + 1*4096
+ * == ~ 122 Kbyte using below heuristic.
+ * In unlikely worst case where bpf progs used all allocations sizes from
+ * non-NMI and from NMI too: ~ 227 Kbyte per cpu.
+ * Initialized, but unused bpf allocator (not bpf map specific one) will
+ * consume ~ 19 Kbyte per cpu.
+ * Typical case will be between 19K and 122K closer to 19K.
+ * bpf progs can and should share bpf_mem_cache when possible.
+ */
+
static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
{
init_irq_work(&c->refill_work, bpf_mem_refill);
+ if (c->unit_size <= 256) {
+ c->low_watermark = 32;
+ c->high_watermark = 96;
+ } else {
+ /* When page_size == 4k, order-0 cache will have low_mark == 2
+ * and high_mark == 6 with batch alloc of 3 individual pages at
+ * a time.
+ * 8k allocs and above low == 1, high == 3, batch == 1.
+ */
+ c->low_watermark = max(32 * 256 / c->unit_size, 1);
+ c->high_watermark = max(96 * 256 / c->unit_size, 3);
+ }
+ c->batch = max((c->high_watermark - c->low_watermark) / 4 * 3, 1);
+
/* To avoid consuming memory assume that 1st run of bpf
* prog won't be doing more than 4 map_update_elem from
* irq disabled region
*/
- alloc_bulk(c, c->unit_size < 256 ? 4 : 1, cpu_to_node(cpu));
+ alloc_bulk(c, c->unit_size <= 256 ? 4 : 1, cpu_to_node(cpu));
/* NMI progs are rare. Assume they have one map_update
* per prog at the very beginning.
@@ -442,7 +468,7 @@ static void notrace *unit_alloc(struct bpf_mem_cache *c)
}
WARN_ON(cnt < 0);
- if (cnt < LOW_WATERMARK)
+ if (cnt < c->low_watermark)
irq_work_raise(c, in_nmi);
return llnode;
}
@@ -471,7 +497,7 @@ static void notrace unit_free(struct bpf_mem_cache *c, void *ptr)
}
WARN_ON(cnt <= 0);
- if (cnt > HIGH_WATERMARK)
+ if (cnt > c->high_watermark)
/* free few objects from current cpu into global kmalloc pool */
irq_work_raise(c, in_nmi);
}
--
2.30.2
