linux-kernel - Re: [PATCH] net/skbuff: silence warnings under memory pressure

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Message-ID: <1567525342.5576.60.camel@lca.pw>
Date:   Tue, 03 Sep 2019 11:42:22 -0400
From:   Qian Cai <cai@....pw>
To:     Michal Hocko <mhocko@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net/skbuff: silence warnings under memory pressure

On Tue, 2019-09-03 at 15:22 +0200, Michal Hocko wrote:
> On Fri 30-08-19 18:15:22, Eric Dumazet wrote:
> > If there is a risk of flooding the syslog, we should fix this generically
> > in mm layer, not adding hundred of __GFP_NOWARN all over the places.
> 
> We do already ratelimit in warn_alloc. If it isn't sufficient then we
> can think of a different parameters. Or maybe it is the ratelimiting
> which doesn't work here. Hard to tell and something to explore.

The time-based ratelimit won't work for skb_build() as when a system under
memory pressure, and the CPU is fast and IO is so slow, it could take a long
time to swap and trigger OOM.

I suppose what happens is those skb_build() allocations are from softirq, and
once one of them failed, it calls printk() which generates more interrupts.
Hence, the infinite loop.