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authorMartynas Pumputis <m@lambda.lt>2019-03-18 18:10:26 +0300
committerDaniel Borkmann <daniel@iogearbox.net>2019-03-18 18:48:25 +0300
commitf01a7dbe98ae4265023fa5d3af0f076f0b18a647 (patch)
tree1a3ed6ee305519403b394ceebde3c87013571f86 /kernel/bpf
parentea239314fe42ace880bdd834256834679346c80e (diff)
downloadlinux-f01a7dbe98ae4265023fa5d3af0f076f0b18a647.tar.xz
bpf: Try harder when allocating memory for large maps
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. Unfortunately, replacing the body of the BPF map memory allocation function with the kvmalloc_node helper function is not an option at this point in time, given 1) kmalloc is non-optional for higher order allocations, and 2) passing __GFP_RETRY_MAYFAIL to the kmalloc would stress the slab allocator too much for large 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@dhcp22.suse.cz/ Signed-off-by: Martynas Pumputis <m@lambda.lt> Acked-by: Yonghong Song <yhs@fb.com> Cc: Michal Hocko <mhocko@suse.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20190318153940.GL8924@dhcp22.suse.cz/
Diffstat (limited to 'kernel/bpf')
-rw-r--r--kernel/bpf/syscall.c22
1 files changed, 15 insertions, 7 deletions
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 62f6bced3a3c..afca36f53c49 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -136,21 +136,29 @@ 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 really just want to fail instead of triggering OOM killer
+ * under memory pressure, therefore we set __GFP_NORETRY to kmalloc,
+ * which is used for lower order allocation requests.
+ *
+ * It has been observed that higher order allocation requests done by
+ * vmalloc with __GFP_NORETRY being set might fail due to not trying
+ * to reclaim memory from the page cache, thus we set
+ * __GFP_RETRY_MAYFAIL to avoid such situations.
*/
- 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);
+ 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,
- __builtin_return_address(0));
+ return __vmalloc_node_flags_caller(size, numa_node,
+ GFP_KERNEL | __GFP_RETRY_MAYFAIL |
+ flags, __builtin_return_address(0));
}
void bpf_map_area_free(void *area)