bpf: Make non-preallocated allocation low priority

GFP_ATOMIC doesn't cooperate well with memcg pressure so far, especially
if we allocate too much GFP_ATOMIC memory. For example, when we set the
memcg limit to limit a non-preallocated bpf memory, the GFP_ATOMIC can
easily break the memcg limit by force charge. So it is very dangerous to
use GFP_ATOMIC in non-preallocated case. One way to make it safe is to
remove __GFP_HIGH from GFP_ATOMIC, IOW, use (__GFP_ATOMIC |
__GFP_KSWAPD_RECLAIM) instead, then it will be limited if we allocate
too much memory. There's a plan to completely remove __GFP_ATOMIC in the
mm side[1], so let's use GFP_NOWAIT instead.

We introduced BPF_F_NO_PREALLOC is because full map pre-allocation is
too memory expensive for some cases. That means removing __GFP_HIGH
doesn't break the rule of BPF_F_NO_PREALLOC, but has the same goal with
it-avoiding issues caused by too much memory. So let's remove it.

This fix can also apply to other run-time allocations, for example, the
allocation in lpm trie, local storage and devmap. So let fix it
consistently over the bpf code

It also fixes a typo in the comment.

[1]. https://lore.kernel.org/linux-mm/163712397076.13692.4727608274002939094@noble.neil.brown.name/

Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: NeilBrown <neilb@suse.de>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Link: https://lore.kernel.org/r/20220709154457.57379-2-laoar.shao@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index c286706..1400561 100644 (file)
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -845,7 +845,7 @@ static struct bpf_dtab_netdev *__dev_map_alloc_node(struct net *net,
        struct bpf_dtab_netdev *dev;
 
        dev = bpf_map_kmalloc_node(&dtab->map, sizeof(*dev),
-                                  GFP_ATOMIC | __GFP_NOWARN,
+                                  GFP_NOWAIT | __GFP_NOWARN,
                                   dtab->map.numa_node);
        if (!dev)
                return ERR_PTR(-ENOMEM);

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 17fb69c..da75784 100644 (file)
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -61,7 +61,7 @@
  *
  * As regular device interrupt handlers and soft interrupts are forced into
  * thread context, the existing code which does
- *   spin_lock*(); alloc(GPF_ATOMIC); spin_unlock*();
+ *   spin_lock*(); alloc(GFP_ATOMIC); spin_unlock*();
  * just works.
  *
  * In theory the BPF locks could be converted to regular spinlocks as well,
@@ -978,7 +978,7 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
                                goto dec_count;
                        }
                l_new = bpf_map_kmalloc_node(&htab->map, htab->elem_size,
-                                            GFP_ATOMIC | __GFP_NOWARN,
+                                            GFP_NOWAIT | __GFP_NOWARN,
                                             htab->map.numa_node);
                if (!l_new) {
                        l_new = ERR_PTR(-ENOMEM);
@@ -996,7 +996,7 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
                } else {
                        /* alloc_percpu zero-fills */
                        pptr = bpf_map_alloc_percpu(&htab->map, size, 8,
-                                                   GFP_ATOMIC | __GFP_NOWARN);
+                                                   GFP_NOWAIT | __GFP_NOWARN);
                        if (!pptr) {
                                kfree(l_new);
                                l_new = ERR_PTR(-ENOMEM);

diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
index 8654fc9..49ef0ce 100644 (file)
--- a/kernel/bpf/local_storage.c
+++ b/kernel/bpf/local_storage.c
@@ -165,7 +165,7 @@ static int cgroup_storage_update_elem(struct bpf_map *map, void *key,
        }
 
        new = bpf_map_kmalloc_node(map, struct_size(new, data, map->value_size),
-                                  __GFP_ZERO | GFP_ATOMIC | __GFP_NOWARN,
+                                  __GFP_ZERO | GFP_NOWAIT | __GFP_NOWARN,
                                   map->numa_node);
        if (!new)
                return -ENOMEM;

diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index f0d05a3..d789e3b 100644 (file)
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -285,7 +285,7 @@ static struct lpm_trie_node *lpm_trie_node_alloc(const struct lpm_trie *trie,
        if (value)
                size += trie->map.value_size;
 
-       node = bpf_map_kmalloc_node(&trie->map, size, GFP_ATOMIC | __GFP_NOWARN,
+       node = bpf_map_kmalloc_node(&trie->map, size, GFP_NOWAIT | __GFP_NOWARN,
                                    trie->map.numa_node);
        if (!node)
                return NULL;