netdev - Re: [PATCH net-next] ip: avoid OOM kills with large UDP sends over loopback

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Message-ID: <20210622125116.44a97a55@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net>
Date:   Tue, 22 Jun 2021 12:51:16 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, willemb@...gle.com,
        dsahern@...il.com, yoshfuji@...ux-ipv6.org, Dave Jones <dsj@...com>
Subject: Re: [PATCH net-next] ip: avoid OOM kills with large UDP sends over
 loopback

On Tue, 22 Jun 2021 12:04:26 -0700 Jakub Kicinski wrote:
> For the UDP case we can either adapt the af_unix approach, and cap head
> size to SKB_MAX_ALLOC or try to allocate the full skb and fall back.
> Having alloc_skb_with_frags() itself re-balance head <> data
> automatically does not feel right, no?

Actually looking closer at the UDP code it appears it only uses the
giant head it allocated if the underlying device doesn't have SG.
We can make the head smaller and probably only improve performance 
for 99% of deployments. I'll send a v2.