netdev - Re: [PATCH 0/6 v3] kvmalloc

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Date:   Thu, 26 Jan 2017 12:58:33 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        marcelo.leitner@...il.com
Subject: Re: [PATCH 0/6 v3] kvmalloc

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