Re: [RFC][PATCH][NET] Fix never pruned tcp out-of-order queue

[Vitaliy Gusev <vgusev@openvz.org>]

> On 15 April 2008 15:59:24 Alexey Kuznetsov wrote:
> Hello!
> 
> > I still think the guards are pretty much the same as before, sorry:)
> 
> Guards inside tcp_prune_queue() are the same exactly.
> 
> But the patch adds the second point where out-of-order queue is discarded.
> It is when the socket is under rcvbuf, but nevertheless skb cannot
> be queued due to system-wide limit. In that case out-of-order queue 
> is dropped and the limits are rechecked.
> 
> 
> > But why not repeat the whole prune for all cases in this case then?
> 
> Collapsing and tuning rcv_ssthresh was done once, they are not guarded
> by rcvbuf check. So, repeating those steps would be useless.
> 
> The only thing is:
> 
> > e.g. you should probably at least repeat the third step (setting
> > pred_flags to 0) too.
> 
> Formally, this is correct. But this is not necessary, pred_flags reset
> is redundant even in the first place. The fast path is not so fast,
> memory limit is checked explicitly there.
> 
> 
> The patch is not perfect. F.e. tcp_prune_ofo_queue() could see empty
> out-of-order queue, in this case the second sk_stream_rmem_schedule()
> is useless and could be skipped. But it is the second order effect.
> 
> I think this will work.

> Thanks for comments. I will correct second call sk_stream_rmem_schedule()
> and resend new patch.

Does tuning window need to consider free TCP memory (something like
tcp_mem[2] - memory_allocated) ?
 
-- 
Thank,
Vitaliy Gusev