linux-kernel - Re: [PATCH net-next v4 4/4] net: tun: track dropped skb via kfree_skb

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Date:   Wed, 2 Mar 2022 21:21:22 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Dongli Zhang <dongli.zhang@...cle.com>
Cc:     dsahern@...il.com, netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, davem@...emloft.net,
        rostedt@...dmis.org, mingo@...hat.com, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, imagedong@...cent.com,
        joao.m.martins@...cle.com, joe.jin@...cle.com, edumazet@...gle.com
Subject: Re: [PATCH net-next v4 4/4] net: tun: track dropped skb via
 kfree_skb_reason()

On Wed, 2 Mar 2022 14:21:31 -0800 Dongli Zhang wrote:
> > because of OOM" is what should be reported. What we were trying to
> > allocate is not very relevant (and can be gotten from the stack trace 
> > if needed).  
> 
> I think OOM is not enough. Although it may not be the case in this patchset,
> sometimes the allocation is failed because we are allocating a large chunk of
> physically continuous pages (kmalloc vs. vmalloc) while there is still plenty of
> memory pages available.
> 
> As a kernel developer, it is very significant for me to identify the specific
> line/function and specific data structure that cause the error. E.g, the bug
> filer may be chasing which line is making trouble.
> 
> It is less likely to SKB_TRIM more than once in a driver function, compared to
> ENOMEM.

Nack, trim is meaningless.