It has been observed that sometimes a higher order memory allocation
for BPF maps fails when there is no obvious memory pressure in a system.
E.g. the map (BPF_MAP_TYPE_LRU_HASH, key=38, value=56, max_elems=524288)
could not be created due to vmalloc unable to allocate 75497472B,
when the system's memory consumption (in MB) was the following:
Total: 3942 Used: 837 (21.24%) Free: 138 Buffers: 239 Cached: 2727
Later analysis [1] by Michal Hocko showed that the vmalloc was not trying
to reclaim memory from the page cache and was failing prematurely due to
__GFP_NORETRY.
Considering dcda9b0471 ("mm, tree wide: replace __GFP_REPEAT by
__GFP_RETRY_MAYFAIL with more useful semantic") and [1], we can replace
__GFP_NORETRY with __GFP_RETRY_MAYFAIL, as it won't invoke OOM killer
and will try harder to fulfil allocation requests.
The change has been tested with the workloads mentioned above and by
observing oom_kill value from /proc/vmstat.
[1]: https://lore.kernel.org/bpf/20190310071318.GW5232@xxxxxxxxxxxxxx/
Signed-off-by: Martynas Pumputis <m@xxxxxxxxx>
---
kernel/bpf/syscall.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 62f6bced3a3c..1b0a057ed6d5 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -136,20 +136,26 @@ static struct bpf_map *find_and_alloc_map(union bpf_attr *attr)
void *bpf_map_area_alloc(size_t size, int numa_node)
{
- /* We definitely need __GFP_NORETRY, so OOM killer doesn't
- * trigger under memory pressure as we really just want to
- * fail instead.
+ /* We definitely need __GFP_NORETRY or __GFP_RETRY_MAYFAIL, so
+ * OOM killer doesn't trigger under memory pressure as we really
+ * just want to fail instead.
*/
- const gfp_t flags = __GFP_NOWARN | __GFP_NORETRY | __GFP_ZERO;
+ const gfp_t flags = __GFP_NOWARN | __GFP_ZERO;
void *area;
if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
- area = kmalloc_node(size, GFP_USER | flags, numa_node);
+ /* To avoid bypassing slab alloc for lower order allocs,
+ * __GFP_NORETRY is used instead of __GFP_RETRY_MAYFAIL.
+ */
+ area = kmalloc_node(size, GFP_USER | __GFP_NORETRY | flags,
+ numa_node);
if (area != NULL)
return area;
}
- return __vmalloc_node_flags_caller(size, numa_node, GFP_KERNEL | flags,
+ return __vmalloc_node_flags_caller(size, numa_node,
+ GFP_KERNEL | __GFP_RETRY_MAYFAIL |
+ flags,
__builtin_return_address(0));
}
--
2.21.0
