netdev - Re: [net-next PATCH 1/3] Revert "icmp: avoid allocating large struct on stack"

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Message-ID: <1483984208.5846.9.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Mon, 09 Jan 2017 09:50:08 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [net-next PATCH 1/3] Revert "icmp: avoid allocating large
 struct on stack"

On Mon, 2017-01-09 at 09:42 -0800, Cong Wang wrote:
> On Mon, Jan 9, 2017 at 7:04 AM, Jesper Dangaard Brouer
> <brouer@...hat.com> wrote:
> > This reverts commit 9a99d4a50cb8 ("icmp: avoid allocating large struct
> > on stack"), because struct icmp_bxm no really a large struct, and
> > allocating and free of this small 112 bytes hurts performance.
> 
> The original commit fixes a warning for large stack usage, icmp_send()
> is deep in the call stack.
> 
> Your optimization for a slow path makes no sense to me.

Do you have the stack trace of this event ?

Even Linus allowed vmalloc() kernel stacks, while it certainly was an
heresy 10 years ago.

I doubt it makes a difference trying to save 104 bytes of kernel stack.