netdev - Re: [PATCH v2] tun: avoid high-order page allocation for packet header

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Date: Tue, 8 Aug 2023 01:22:51 +0000
From: "Erdogan, Tahsin" <trdgn@...zon.com>
To: "edumazet@...gle.com" <edumazet@...gle.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
	"davem@...emloft.net" <davem@...emloft.net>, "kuba@...nel.org"
	<kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v2] tun: avoid high-order page allocation for packet
 header

On Tue, 2023-08-01 at 12:16 +0200, Eric Dumazet wrote:
> On Tue, Aug 1, 2023 at 11:37 AM Eric Dumazet <edumazet@...gle.com>
> wrote:
> > On Tue, Aug 1, 2023 at 1:07 AM Tahsin Erdogan <trdgn@...zon.com>
> > wrote:
> > > When GSO is not enabled and a packet is transmitted via writev(),
> > > all
> > > payload is treated as header which requires a contiguous memory
> > > allocation.
> > > This allocation request is harder to satisfy, and may even fail
> > > if there is
> > > enough fragmentation.
> > > 
> > > Note that sendmsg() code path limits the linear copy length, so
> > > this change
> > > makes writev() and sendmsg() more consistent.
> > > 
> > > Signed-off-by: Tahsin Erdogan <trdgn@...zon.com>
> > > ---
> > 
> > I will have to tweak one existing packetdrill test, nothing major.
> > 
> > Tested-by: Eric Dumazet <edumazet@...gle.com>
> > Reviewed-by: Eric Dumazet <edumazet@...gle.com>
> 
> I have to take this back, sorry.
> 
> We need to change alloc_skb_with_frags() and tun.c to attempt
> high-order allocations,
> otherwise tun users sending very large buffers will regress.
> (Even if this _could_ fail as you pointed out if memory is
> tight/fragmented)
> 
> I am working to make the change in alloc_skb_with_frags() and in tun,
> we can apply your patch after this prereq.

Hi Eric, I believe your changes are merged. Are we good to apply my
patch next?