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authorMartin KaFai Lau <kafai@fb.com>2020-02-07 00:18:10 -0800
committerDaniel Borkmann <daniel@iogearbox.net>2020-02-07 23:01:41 +0100
commit88d6f130e5632bbf419a2e184ec7adcbe241260b (patch)
treef5eef5513c35757cf56d82496e670a3e4033ac55 /net
parent5d3919a953c3c96c02fc7a337f8376cde43ae31f (diff)
bpf: Improve bucket_log calculation logic
It was reported that the max_t, ilog2, and roundup_pow_of_two macros have exponential effects on the number of states in the sparse checker. This patch breaks them up by calculating the "nbuckets" first so that the "bucket_log" only needs to take ilog2(). In addition, Linus mentioned: Patch looks good, but I'd like to point out that it's not just sparse. You can see it with a simple make net/core/bpf_sk_storage.i grep 'smap->bucket_log = ' net/core/bpf_sk_storage.i | wc and see the end result: 1 365071 2686974 That's one line (the assignment line) that is 2,686,974 characters in length. Now, sparse does happen to react particularly badly to that (I didn't look to why, but I suspect it's just that evaluating all the types that don't actually ever end up getting used ends up being much more expensive than it should be), but I bet it's not good for gcc either. Fixes: 6ac99e8f23d4 ("bpf: Introduce bpf sk local storage") Reported-by: Randy Dunlap <rdunlap@infradead.org> Reported-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Martin KaFai Lau <kafai@fb.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com> Link: https://lore.kernel.org/bpf/20200207081810.3918919-1-kafai@fb.com
Diffstat (limited to 'net')
-rw-r--r--net/core/bpf_sk_storage.c5
1 files changed, 3 insertions, 2 deletions
diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
index 458be6b3eda9..3ab23f698221 100644
--- a/net/core/bpf_sk_storage.c
+++ b/net/core/bpf_sk_storage.c
@@ -643,9 +643,10 @@ static struct bpf_map *bpf_sk_storage_map_alloc(union bpf_attr *attr)
return ERR_PTR(-ENOMEM);
bpf_map_init_from_attr(&smap->map, attr);
+ nbuckets = roundup_pow_of_two(num_possible_cpus());
/* Use at least 2 buckets, select_bucket() is undefined behavior with 1 bucket */
- smap->bucket_log = max_t(u32, 1, ilog2(roundup_pow_of_two(num_possible_cpus())));
- nbuckets = 1U << smap->bucket_log;
+ nbuckets = max_t(u32, 2, nbuckets);
+ smap->bucket_log = ilog2(nbuckets);
cost = sizeof(*smap->buckets) * nbuckets + sizeof(*smap);
ret = bpf_map_charge_init(&smap->map.memory, cost);