netdev - Re: [PATCH] kthread: NUMA aware kthread_create_on

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Date:	Mon, 29 Nov 2010 00:37:04 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>, Tejun Heo <tj@...nel.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] kthread: NUMA aware kthread_create_on_cpu()

Le lundi 29 novembre 2010 à 00:01 +0100, Andi Kleen a écrit :
> On Sun, Nov 28, 2010 at 11:51:51PM +0100, Eric Dumazet wrote:
> > > Also this messes up the policy of the caller process. You really
> > > need to save/restore it.
> > 
> > Well, caller process duty is to create kthreads in a loop.
> 
> In this case any other allocations it may do
>  are still on those
> nodes.

As I said, it does only create_kthread() calls, and no "other
allocations".

while (!list_empty(&kthread_create_list)) {
      struct kthread_create_info *create;

      create = list_entry(kthread_create_list.next,
                          struct kthread_create_info, list);
      list_del_init(&create->list);
      spin_unlock(&kthread_create_lock);

      create_kthread(create);

      spin_lock(&kthread_create_lock);
}





> 
> > > Problem is that this ends up in architecture specific code
> > > for the stack, so may be a larger patch.
> > 
> > I suggest arches that need slab to allocate kthread stacks do the
> > appropriate changes, because I am not able to make them myself.
> > 
> > On x86, we use page allocator only, so NUMA mempolicy is used.
> 
> task_struct is always allocated from slab.

Hmm, I meant stack (the thing that might be trashed a lot in ksoftirqd),
so it is included in struct thread_info

And this one uses __get_free_pages(GFP_KERNEL, THREAD_SIZE_ORDER) from
alloc_thread_info()


By the way, I re-tested my original patch (MPOL_BIND) on x86_32

# cat /proc/buddyinfo 
Node 0, zone      DMA      0      1      0      1      2      1      1      0      1      1      3 
Node 0, zone   Normal     22     14     10      3      2      3      4      2      3      2    165 
Node 0, zone  HighMem     41     35    346    223    124    140     40     19      2      0    143 
Node 1, zone  HighMem     21      7      8      4    217     97     33     11      3      1    415 

And got correct stacks. Are you sure we must use PREFERRED ?



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