linux-kernel - Re: [PATCH net 0/3] Fix for BPF devmap percpu allocation splat

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Date:   Wed, 18 Oct 2017 16:45:08 -0500
From:   Dennis Zhou <dennisszhou@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Daniel Borkmann <daniel@...earbox.net>, davem@...emloft.net,
        ast@...nel.org, john.fastabend@...il.com, mark.rutland@....com,
        richard@....at, sp3485@...umbia.edu, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 0/3] Fix for BPF devmap percpu allocation splat

Hi Daniel and Tejun,

On Wed, Oct 18, 2017 at 06:25:26AM -0700, Tejun Heo wrote:
> > Daniel Borkmann (3):
> >   mm, percpu: add support for __GFP_NOWARN flag
> 
> This looks fine.
> 

Looks good to me too.

> >   bpf: fix splat for illegal devmap percpu allocation
> >   bpf: do not test for PCPU_MIN_UNIT_SIZE before percpu allocations
> 
> These look okay too but if it helps percpu allocator can expose the
> maximum size / alignment supported to take out the guessing game too.
> 

I can add this once we've addressed the below if we want to.

> Also, the reason why PCPU_MIN_UNIT_SIZE is what it is is because
> nobody needed anything bigger.  Increasing the size doesn't really
> cost much at least on 64bit archs.  Is that something we want to be
> considering?
> 

I'm not sure I see the reason we can't match the minimum allocation size
with the unit size? It seems weird to arbitrate the maximum allocation
size given a lower bound on the unit size.

Thanks,
Dennis