On 3/8/19 9:44 AM, Michal Hocko wrote:
On Fri 08-03-19 09:08:57, Martynas Pumputis wrote:
It has been observed that sometimes 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 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
Hmm 75MB is quite large and much larger than the slab/page allocator
cann provide so this is not really a fragmentation issue. Vmalloc does
respect noretry but considering that there shouldn't be a large memory
pressure I wonder how NORETRY managed to fail the allocation. Do you
happen to have the allocation failure report?
I got /proc/{meminfo,vmstat,vmallocinfo} just after the allocation has
failed:
https://gist.github.com/brb/62092c1d83daa6527271b88f0352e32d
Let me know if more info is required, I can reproduce the failure. Thanks.
Btw. is there any real reason to opencode and duplicate kvmalloc logic
here? In other words why not simply make bpf_map_area_alloc use
kvmalloc_node with GFP_KERNEL?
Considering dcda9b0471 ("mm, tree wide: replace __GFP_REPEAT by
__GFP_RETRY_MAYFAIL with more useful semantic") 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.
Signed-off-by: Martynas Pumputis <m@xxxxxxxxx>
---
kernel/bpf/syscall.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 62f6bced3a3c..eb5cefe44af3 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -136,11 +136,11 @@ 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_RETRY_MAYFAIL | __GFP_ZERO;
void *area;
if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
--
2.21.0
