LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	linux-mm@kvack.org, David Miller <davem@davemloft.net>
Subject: Re: [PATCH 9/9] net: vm deadlock avoidance core
Date: Wed, 17 Jan 2007 10:07:28 +0100	[thread overview]
Message-ID: <1169024848.22935.109.camel@twins> (raw)
In-Reply-To: <20070117045426.GA20921@2ka.mipt.ru>

On Wed, 2007-01-17 at 07:54 +0300, Evgeniy Polyakov wrote:
> On Tue, Jan 16, 2007 at 05:08:15PM +0100, Peter Zijlstra (a.p.zijlstra@chello.nl) wrote:
> > On Tue, 2007-01-16 at 18:33 +0300, Evgeniy Polyakov wrote:
> > > On Tue, Jan 16, 2007 at 02:47:54PM +0100, Peter Zijlstra (a.p.zijlstra@chello.nl) wrote:
> > > > > > +	if (unlikely(skb->emergency))
> > > > > > +		current->flags |= PF_MEMALLOC;
> > > > > 
> > > > > Access to 'current' in netif_receive_skb()???
> > > > > Why do you want to work with, for example keventd?
> > > > 
> > > > Can this run in keventd?
> > > 
> > > Initial netchannel implementation by Kelly Daly (IBM) worked in keventd
> > > (or dedicated kernel thread, I do not recall).
> > > 
> > > > I thought this was softirq context and thus this would either run in a
> > > > borrowed context or in ksoftirqd. See patch 3/9.
> > > 
> > > And how are you going to access 'current' in softirq?
> > > 
> > > netif_receive_skb() can also be called from a lot of other places
> > > including keventd and/or different context - it is permitted to call it
> > > everywhere to process packet.
> > > 
> > > I meant that you break the rule accessing 'current' in that context.
> > 
> > Yeah, I know, but as long as we're not actually in hard irq context
> > current does point to the task_struct in charge of current execution and
> > as long as we restore whatever was in the flags field before we started
> > poking, nothing can go wrong.
> > 
> > So, yes this is unconventional, but it does work as expected.
> > 
> > As for breaking, 3/9 makes it legal.
> 
> You operate with 'current' in different contexts without any locks which
> looks racy and even is not allowed. What will be 'current' for
> netif_rx() case, which schedules softirq from hard irq context -
> ksoftirqd, why do you want to set its flags?

I don't touch current in hardirq context, do I (if I did, that is indeed
a mistake)?

In all other contexts, current is valid.

> > > I meant that you can just mark process which created such socket as
> > > PF_MEMALLOC, and clone that flag on forks and other relatest calls without 
> > > all that checks for 'current' in different places.
> > 
> > Ah, thats the wrong level to think here, these processes never reach
> > user-space - nor should these sockets.
> 
> You limit this just to send an ack?
> What about 'level-7' ack as you described in introduction?

Take NFS, it does full data traffic in kernel.

> > Also, I only want the processing of the actual network packet to be able
> > to eat the reserves, not any other thing that might happen in that
> > context.
> > 
> > And since network processing is mostly done in softirq context I must
> > mark these sections like I did.
> 
> You artificially limit system to just add a reserve to generate one ack.
> For that purpose you do not need to have all those flags - just reseve
> some data in network core and use it when system is in OOM (or reclaim)
> for critical data pathes.

How would that end up being different, I would have to replace all
allocations done in the full network processing path.

This seems a much less invasive method, all the (allocation) code can
stay the way it is and use the normal allocation functions.

> > > > > > +		/*
> > > > > > +		   decrease window size..
> > > > > > +		   tcp_enter_quickack_mode(sk);
> > > > > > +		*/
> > > > > 
> > > > > How does this decrease window size?
> > > > > Maybe ack scheduling would be better handled by inet_csk_schedule_ack()
> > > > > or just directly send an ack, which in turn requires allocation, which
> > > > > can be bound to this received frame processing...
> > > > 
> > > > It doesn't, I thought that it might be a good idea doing that, but never
> > > > got around to actually figuring out how to do it.
> > > 
> > > tcp_send_ack()?
> > > 
> > 
> > does that shrink the window automagically?
> 
> Yes, it updates window, but having ack generated in that place is
> actually very wrong. In that place system has not processed incoming
> packet yet, so it can not generate correct ACK for received frame at
> all. And it seems that the only purpose of the whole patchset is to
> generate that poor ack - reseve 2007 ack packets (MAX_TCP_HEADER) 
> in system startup and reuse them when you are under memory pressure.

Right, I suspected something like that; hence I wanted to just shrink
the window. Anyway, this is not a very important issue.


  reply	other threads:[~2007-01-17  9:10 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-16  9:45 [PATCH 0/9] VM deadlock avoidance -v10 Peter Zijlstra
2007-01-16  9:45 ` [PATCH 1/9] mm: page allocation rank Peter Zijlstra
2007-01-16  9:45 ` [PATCH 2/9] mm: slab allocation fairness Peter Zijlstra
2007-01-16  9:46 ` [PATCH 3/9] mm: allow PF_MEMALLOC from softirq context Peter Zijlstra
2007-01-16  9:46 ` [PATCH 4/9] mm: serialize access to min_free_kbytes Peter Zijlstra
2007-01-16  9:46 ` [PATCH 5/9] mm: emergency pool Peter Zijlstra
2007-01-16  9:46 ` [PATCH 6/9] mm: __GFP_EMERGENCY Peter Zijlstra
2007-01-16  9:46 ` [PATCH 7/9] mm: allow mempool to fall back to memalloc reserves Peter Zijlstra
2007-01-16  9:46 ` [PATCH 8/9] slab: kmem_cache_objs_to_pages() Peter Zijlstra
2007-01-16  9:46 ` [PATCH 9/9] net: vm deadlock avoidance core Peter Zijlstra
2007-01-16 13:25   ` Evgeniy Polyakov
2007-01-16 13:47     ` Peter Zijlstra
2007-01-16 15:33       ` Evgeniy Polyakov
2007-01-16 16:08         ` Peter Zijlstra
2007-01-17  4:54           ` Evgeniy Polyakov
2007-01-17  9:07             ` Peter Zijlstra [this message]
2007-01-18 10:41               ` Evgeniy Polyakov
2007-01-18 12:18                 ` Peter Zijlstra
2007-01-18 13:58                   ` Possible ways of dealing with OOM conditions Evgeniy Polyakov
2007-01-18 15:10                     ` Peter Zijlstra
2007-01-18 15:50                       ` Evgeniy Polyakov
2007-01-18 17:31                         ` Peter Zijlstra
2007-01-18 18:34                           ` Evgeniy Polyakov
2007-01-19 12:53                             ` Peter Zijlstra
2007-01-19 22:56                               ` Evgeniy Polyakov
2007-01-20 22:36                                 ` Rik van Riel
2007-01-21  1:46                                   ` Evgeniy Polyakov
2007-01-21  2:14                                     ` Evgeniy Polyakov
2007-01-21 16:30                                     ` Rik van Riel
2007-01-19 17:54                           ` Christoph Lameter
2007-01-17  9:12 ` [PATCH 0/9] VM deadlock avoidance -v10 Pavel Machek
2007-01-17  9:20   ` Peter Zijlstra

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1169024848.22935.109.camel@twins \
    --to=a.p.zijlstra@chello.nl \
    --cc=davem@davemloft.net \
    --cc=johnpol@2ka.mipt.ru \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=netdev@vger.kernel.org \
    --subject='Re: [PATCH 9/9] net: vm deadlock avoidance core' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).