netdev - Re: [PATCH 2/3] xfrm: Increase the garbage collector threshold

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Message-ID: <1387204190.25449.68.camel@sakura.staff.proxad.net>
Date:	Mon, 16 Dec 2013 15:29:50 +0100
From:	Maxime Bizon <mbizon@...ebox.fr>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	David Miller <davem@...emloft.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	netdev@...r.kernel.org
Subject: Re: [PATCH 2/3] xfrm: Increase the garbage collector threshold


On Mon, 2013-12-16 at 12:51 +0100, Steffen Klassert wrote:

> >   while :; do wget -O /dev/null http://remote_host/; done
> > 
> > I was surprised to see it fails after only 1024 requests (ENOBUF on
> > connect), and how long I had to wait to be able to do new requests.
> > 
> > After debugging I saw that the xfrm gc was called but was not able to
> > release anything.
> > 
> > after running "ip route flush cache", which forces all ipv4 dst entries
> > to be released, suddenly the xfrm gc had something to free, and xfrm
> > entry count went to zero.
> 
> Well, "ip route flush cache" bumps the rt_genid what marks all
> routes as invalid. The xfrm garbage collector will notice this
> on the next run and deletes all invalid cached routes.
> 
> Garbage collecting is different from flushing, it only removes
> stale routes and keeps everything that was used recently. That's
> the whole point of this caching, we cache recently used IPsec
> routes to avoid a slow path lookup.

ok I don't know this part of the code at all.

but if it is only a *cache*, then it should not limit any new
allocations for the reason that the cache is full, it should take slow
path instead.

-- 
Maxime


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