From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f44.google.com (mail-pa0-f44.google.com [209.85.220.44]) by kanga.kvack.org (Postfix) with ESMTP id 4C5C96B0253 for ; Fri, 9 Oct 2015 11:54:39 -0400 (EDT) Received: by pacex6 with SMTP id ex6so90463849pac.0 for ; Fri, 09 Oct 2015 08:54:39 -0700 (PDT) Received: from mail-pa0-f44.google.com (mail-pa0-f44.google.com. [209.85.220.44]) by mx.google.com with ESMTPS id qa3si3521080pbc.31.2015.10.09.08.54.38 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 09 Oct 2015 08:54:38 -0700 (PDT) Received: by pabve7 with SMTP id ve7so31624349pab.2 for ; Fri, 09 Oct 2015 08:54:38 -0700 (PDT) Content-Type: multipart/alternative; boundary="Apple-Mail=_22333FEE-64E2-41A4-8C50-C3841C7CAF21" Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2104\)) Subject: Re: [ovs-dev] [PATCH] ovs: do not allocate memory from offline numa node From: Jarno Rajahalme In-Reply-To: Date: Fri, 9 Oct 2015 08:54:35 -0700 Message-Id: References: <20151002101822.12499.27658.stgit@buzz> <56128238.8010305@suse.cz> <5612DCC8.4040605@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Jesse Gross Cc: Alexander Duyck , Vlastimil Babka , Konstantin Khlebnikov , "dev@openvswitch.org" , Pravin Shelar , "David S. Miller" , netdev , Linux Kernel Mailing List , linux-mm@kvack.org --Apple-Mail=_22333FEE-64E2-41A4-8C50-C3841C7CAF21 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > On Oct 8, 2015, at 4:03 PM, Jesse Gross wrote: >=20 > On Wed, Oct 7, 2015 at 10:47 AM, Jarno Rajahalme = > wrote: >>=20 >>> On Oct 6, 2015, at 6:01 PM, Jesse Gross wrote: >>>=20 >>> On Mon, Oct 5, 2015 at 1:25 PM, Alexander Duyck >>> wrote: >>>> On 10/05/2015 06:59 AM, Vlastimil Babka wrote: >>>>>=20 >>>>> On 10/02/2015 12:18 PM, Konstantin Khlebnikov wrote: >>>>>>=20 >>>>>> When openvswitch tries allocate memory from offline numa node 0: >>>>>> stats =3D kmem_cache_alloc_node(flow_stats_cache, GFP_KERNEL | = __GFP_ZERO, >>>>>> 0) >>>>>> It catches VM_BUG_ON(nid < 0 || nid >=3D MAX_NUMNODES || = !node_online(nid)) >>>>>> [ replaced with VM_WARN_ON(!node_online(nid)) recently ] in = linux/gfp.h >>>>>> This patch disables numa affinity in this case. >>>>>>=20 >>>>>> Signed-off-by: Konstantin Khlebnikov >>>>>=20 >>>>>=20 >>>>> ... >>>>>=20 >>>>>> diff --git a/net/openvswitch/flow_table.c = b/net/openvswitch/flow_table.c >>>>>> index f2ea83ba4763..c7f74aab34b9 100644 >>>>>> --- a/net/openvswitch/flow_table.c >>>>>> +++ b/net/openvswitch/flow_table.c >>>>>> @@ -93,7 +93,8 @@ struct sw_flow *ovs_flow_alloc(void) >>>>>>=20 >>>>>> /* Initialize the default stat node. */ >>>>>> stats =3D kmem_cache_alloc_node(flow_stats_cache, >>>>>> - GFP_KERNEL | __GFP_ZERO, 0); >>>>>> + GFP_KERNEL | __GFP_ZERO, >>>>>> + node_online(0) ? 0 : NUMA_NO_NODE); >>>>>=20 >>>>>=20 >>>>> Stupid question: can node 0 become offline between this check, and = the >>>>> VM_WARN_ON? :) BTW what kind of system has node 0 offline? >>>>=20 >>>>=20 >>>> Another question to ask would be is it possible for node 0 to be = online, but >>>> be a memoryless node? >>>>=20 >>>> I would say you are better off just making this call = kmem_cache_alloc. I >>>> don't see anything that indicates the memory has to come from node = 0, so >>>> adding the extra overhead doesn't provide any value. >>>=20 >>> I agree that this at least makes me wonder, though I actually have >>> concerns in the opposite direction - I see assumptions about this >>> being on node 0 in net/openvswitch/flow.c. >>>=20 >>> Jarno, since you original wrote this code, can you take a look to = see >>> if everything still makes sense? >>=20 >> We keep the pre-allocated stats node at array index 0, which is = initially used by all CPUs, but if CPUs from multiple numa nodes start = updating the stats, we allocate additional stats nodes (up to one per = numa node), and the CPUs on node 0 keep using the preallocated entry. If = stats cannot be allocated from CPUs local node, then those CPUs keep = using the entry at index 0. Currently the code in net/openvswitch/flow.c = will try to allocate the local memory repeatedly, which may not be = optimal when there is no memory at the local node. >>=20 >> Allocating the memory for the index 0 from other than node 0, as = discussed here, just means that the CPUs on node 0 will keep on using = non-local memory for stats. In a scenario where there are CPUs on two = nodes (0, 1), but only the node 1 has memory, a shared flow entry will = still end up having separate memory allocated for both nodes, but both = of the nodes would be at node 1. However, there is still a high = likelihood that the memory allocations would not share a cache line, = which should prevent the nodes from invalidating each other=E2=80=99s = caches. Based on this I do not see a problem relaxing the memory = allocation for the default stats node. If node 0 has memory, however, it = would be better to allocate the memory from node 0. >=20 > Thanks for going through all of that. >=20 > It seems like the question that is being raised is whether it actually > makes sense to try to get the initial memory on node 0, especially > since it seems to introduce some corner cases? Is there any reason why > the flow is more likely to hit node 0 than a randomly chosen one? > (Assuming that this is a multinode system, otherwise it's kind of a > moot point.) We could have a separate pointer to the default allocated > memory, so it wouldn't conflict with memory that was intentionally > allocated for node 0. It would still be preferable to know from which node the default stats = node was allocated, and store it in the appropriate pointer in the = array. We could then add a new =E2=80=9Cdefault stats node index=E2=80=9D = that would be used to locate the node in the array of pointers we = already have. That way we would avoid extra allocation and processing of = the default stats node. Jarno --Apple-Mail=_22333FEE-64E2-41A4-8C50-C3841C7CAF21 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8
On Oct 8, 2015, at 4:03 PM, Jesse Gross <jesse@nicira.com> = wrote:

On Wed, Oct 7, 2015 at 10:47 AM, Jarno Rajahalme = <jrajahalme@nicira.com> wrote:

On Oct 6, 2015, at 6:01 = PM, Jesse Gross <jesse@nicira.com> wrote:

On= Mon, Oct 5, 2015 at 1:25 PM, Alexander Duyck
<alexander.duyck@gmail.com> wrote:
On 10/05/2015 06:59 AM, = Vlastimil Babka wrote:

On 10/02/2015 12:18 PM, Konstantin Khlebnikov = wrote:

When openvswitch tries allocate memory from offline numa node = 0:
stats =3D kmem_cache_alloc_node(flow_stats_cache, = GFP_KERNEL | __GFP_ZERO,
0)
It catches = VM_BUG_ON(nid < 0 || nid >=3D MAX_NUMNODES || = !node_online(nid))
[ replaced with = VM_WARN_ON(!node_online(nid)) recently ] in linux/gfp.h
This= patch disables numa affinity in this case.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>


...

diff = --git a/net/openvswitch/flow_table.c b/net/openvswitch/flow_table.c
index f2ea83ba4763..c7f74aab34b9 100644
--- = a/net/openvswitch/flow_table.c
+++ = b/net/openvswitch/flow_table.c
@@ -93,7 +93,8 @@ struct = sw_flow *ovs_flow_alloc(void)

    /* Initialize the default stat node. = */
    stats =3D = kmem_cache_alloc_node(flow_stats_cache,
- =             &n= bsp;        GFP_KERNEL | = __GFP_ZERO, 0);
+ =             &n= bsp;        GFP_KERNEL | = __GFP_ZERO,
+ =             &n= bsp;        node_online(0) ? 0 : = NUMA_NO_NODE);


Stupid question: can node 0 become offline between this = check, and the
VM_WARN_ON? :) BTW what kind of system has = node 0 offline?


Another question to ask would be is it possible for node 0 to = be online, but
be a memoryless node?

I would say you are better off just making this call = kmem_cache_alloc.  I
don't see anything that = indicates the memory has to come from node 0, so
adding = the extra overhead doesn't provide any value.

I agree that this at least makes = me wonder, though I actually have
concerns in the opposite = direction - I see assumptions about this
being on node 0 = in net/openvswitch/flow.c.

Jarno, since you = original wrote this code, can you take a look to see
if = everything still makes sense?

We= keep the pre-allocated stats node at array index 0, which is initially = used by all CPUs, but if CPUs from multiple numa nodes start updating = the stats, we allocate additional stats nodes (up to one per numa node), = and the CPUs on node 0 keep using the preallocated entry. If stats = cannot be allocated from CPUs local node, then those CPUs keep using the = entry at index 0. Currently the code in net/openvswitch/flow.c will try = to allocate the local memory repeatedly, which may not be optimal when = there is no memory at the local node.

Allocating the memory for the index 0 from other than node 0, = as discussed here, just means that the CPUs on node 0 will keep on using = non-local memory for stats. In a scenario where there are CPUs on two = nodes (0, 1), but only the node 1 has memory, a shared flow entry will = still end up having separate memory allocated for both nodes, but both = of the nodes would be at node 1. However, there is still a high = likelihood that the memory allocations would not share a cache line, = which should prevent the nodes from invalidating each other=E2=80=99s = caches. Based on this I do not see a problem relaxing the memory = allocation for the default stats node. If node 0 has memory, however, it = would be better to allocate the memory from node 0.

Thanks for going through = all of that.

It seems like the question = that is being raised is whether it actually
makes sense to try to get the initial memory on = node 0, especially
since it seems to = introduce some corner cases? Is there any reason why
the flow is more likely to hit node 0 than a = randomly chosen one?
(Assuming that this is a = multinode system, otherwise it's kind of a
moot point.) We could have a separate pointer to = the default allocated
memory, so it wouldn't = conflict with memory that was intentionally
allocated for node = 0.

It = would still be preferable to know from which node the default stats node = was allocated, and store it in the appropriate pointer in the array. We = could then add a new =E2=80=9Cdefault stats node index=E2=80=9D that = would be used to locate the node in the array of pointers we already = have. That way we would avoid extra allocation and processing of the = default stats node.

  Jarno

= --Apple-Mail=_22333FEE-64E2-41A4-8C50-C3841C7CAF21-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org