Re: [PATCH 0/6 v3] kvmalloc

[Michal Hocko <mhocko@kernel.org>]

On Thu 26-01-17 12:33:55, Daniel Borkmann wrote:
> On 01/26/2017 11:08 AM, Michal Hocko wrote:
[...]
> > If you disagree I can drop the bpf part of course...
> 
> If we could consolidate these spots with kvmalloc() eventually, I'm
> all for it. But even if __GFP_NORETRY is not covered down to all
> possible paths, it kind of does have an effect already of saying
> 'don't try too hard', so would it be harmful to still keep that for
> now? If it's not, I'd personally prefer to just leave it as is until
> there's some form of support by kvmalloc() and friends.

Well, you can use kvmalloc(size, GFP_KERNEL|__GFP_NORETRY). It is not
disallowed. It is not _supported_ which means that if it doesn't work as
you expect you are on your own. Which is actually the situation right
now as well. But I still think that this is just not right thing to do.
Even though it might happen to work in some cases it gives a false
impression of a solution. So I would rather go with
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 8697f43cf93c..a6dc4d596f14 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -53,6 +53,11 @@ void bpf_register_map_type(struct bpf_map_type_list *tl)
 
 void *bpf_map_area_alloc(size_t size)
 {
+	/*
+	 * FIXME: we would really like to not trigger the OOM killer and rather
+	 * fail instead. This is not supported right now. Please nag MM people
+	 * if these OOM start bothering people.
+	 */
 	return kvzalloc(size, GFP_USER);
 }
 

-- 
Michal Hocko
SUSE Labs