Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 719ADC433EF for ; Tue, 16 Nov 2021 02:58:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 565E0619E8 for ; Tue, 16 Nov 2021 02:58:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240620AbhKPDA5 (ORCPT ); Mon, 15 Nov 2021 22:00:57 -0500 Received: from out30-54.freemail.mail.aliyun.com ([115.124.30.54]:58060 "EHLO out30-54.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241467AbhKPDAa (ORCPT ); Mon, 15 Nov 2021 22:00:30 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04395;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0UwnkBMe_1637031451; Received: from 30.21.164.20(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0UwnkBMe_1637031451) by smtp.aliyun-inc.com(127.0.0.1); Tue, 16 Nov 2021 10:57:32 +0800 Message-ID: Date: Tue, 16 Nov 2021 10:58:18 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Subject: Re: [PATCH v3] mm: migrate: Support multiple target nodes demotion To: Yang Shi Cc: Andrew Morton , Huang Ying , Dave Hansen , Zi Yan , Oscar Salvador , zhongjiang-ali@linux.alibaba.com, Xunlei Pang , Linux MM , Linux Kernel Mailing List References: From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/11/16 3:06, Yang Shi wrote: > On Sun, Nov 14, 2021 at 6:40 AM Baolin Wang > wrote: >> >> >> >> On 2021/11/13 3:05, Yang Shi wrote: >>> On Thu, Nov 11, 2021 at 6:28 PM Baolin Wang >>> wrote: >>>> >>>> We have some machines with multiple memory types like below, which >>>> have one fast (DRAM) memory node and two slow (persistent memory) memory >>>> nodes. According to current node demotion policy, if node 0 fills up, >>>> its memory should be migrated to node 1, when node 1 fills up, its >>>> memory will be migrated to node 2: node 0 -> node 1 -> node 2 ->stop. >>>> >>>> But this is not efficient and suitbale memory migration route >>>> for our machine with multiple slow memory nodes. Since the distance >>>> between node 0 to node 1 and node 0 to node 2 is equal, and memory >>>> migration between slow memory nodes will increase persistent memory >>>> bandwidth greatly, which will hurt the whole system's performance. >>>> >>>> Thus for this case, we can treat the slow memory node 1 and node 2 >>>> as a whole slow memory region, and we should migrate memory from >>>> node 0 to node 1 and node 2 if node 0 fills up. >>>> >>>> This patch changes the node_demotion data structure to support multiple >>>> target nodes, and establishes the migration path to support multiple >>>> target nodes with validating if the node distance is the best or not. >>>> >>>> available: 3 nodes (0-2) >>>> node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 >>>> node 0 size: 62153 MB >>>> node 0 free: 55135 MB >>>> node 1 cpus: >>>> node 1 size: 127007 MB >>>> node 1 free: 126930 MB >>>> node 2 cpus: >>>> node 2 size: 126968 MB >>>> node 2 free: 126878 MB >>>> node distances: >>>> node 0 1 2 >>>> 0: 10 20 20 >>>> 1: 20 10 20 >>>> 2: 20 20 10 >>>> >>>> Signed-off-by: Baolin Wang >>>> --- >>>> Changes from v2: >>>> - Redefine the DEMOTION_TARGET_NODES macro according to the >>>> MAX_NUMNODES. >>>> - Change node_demotion to a pointer and allocate it dynamically. >>>> >>>> Changes from v1: >>>> - Add a new patch to allocate the node_demotion dynamically. >>>> - Update some comments. >>>> - Simplify some variables' name. >>>> >>>> Changes from RFC v2: >>>> - Change to 'short' type for target nodes array. >>>> - Remove nodemask instead selecting target node directly. >>>> - Add WARN_ONCE() if the target nodes exceed the maximum value. >>>> >>>> Changes from RFC v1: >>>> - Re-define the node_demotion structure. >>>> - Set up multiple target nodes by validating the node distance. >>>> - Add more comments. >>>> --- >>>> mm/migrate.c | 167 ++++++++++++++++++++++++++++++++++++++++++++++------------- >>>> 1 file changed, 132 insertions(+), 35 deletions(-) >>>> >>>> diff --git a/mm/migrate.c b/mm/migrate.c >>>> index cf25b00..9b8a813 100644 >>>> --- a/mm/migrate.c >>>> +++ b/mm/migrate.c >>>> @@ -50,6 +50,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> >>>> #include >>>> >>>> @@ -1119,12 +1120,25 @@ static int __unmap_and_move(struct page *page, struct page *newpage, >>>> * >>>> * This is represented in the node_demotion[] like this: >>>> * >>>> - * { 1, // Node 0 migrates to 1 >>>> - * 2, // Node 1 migrates to 2 >>>> - * -1, // Node 2 does not migrate >>>> - * 4, // Node 3 migrates to 4 >>>> - * 5, // Node 4 migrates to 5 >>>> - * -1} // Node 5 does not migrate >>>> + * { nr=1, nodes[0]=1 }, // Node 0 migrates to 1 >>>> + * { nr=1, nodes[0]=2 }, // Node 1 migrates to 2 >>>> + * { nr=0, nodes[0]=-1 }, // Node 2 does not migrate >>>> + * { nr=1, nodes[0]=4 }, // Node 3 migrates to 4 >>>> + * { nr=1, nodes[0]=5 }, // Node 4 migrates to 5 >>>> + * { nr=0, nodes[0]=-1 }, // Node 5 does not migrate >>>> + * >>>> + * Moreover some systems may have multiple slow memory nodes. >>>> + * Suppose a system has one socket with 3 memory nodes, node 0 >>>> + * is fast memory type, and node 1/2 both are slow memory >>>> + * type, and the distance between fast memory node and slow >>>> + * memory node is same. So the migration path should be: >>>> + * >>>> + * 0 -> 1/2 -> stop >>>> + * >>>> + * This is represented in the node_demotion[] like this: >>>> + * { nr=2, {nodes[0]=1, nodes[1]=2} }, // Node 0 migrates to node 1 and node 2 >>>> + * { nr=0, nodes[0]=-1, }, // Node 1 dose not migrate >>>> + * { nr=0, nodes[0]=-1, }, // Node 2 does not migrate >>>> */ >>>> >>>> /* >>>> @@ -1135,8 +1149,20 @@ static int __unmap_and_move(struct page *page, struct page *newpage, >>>> * must be held over all reads to ensure that no cycles are >>>> * observed. >>>> */ >>>> -static int node_demotion[MAX_NUMNODES] __read_mostly = >>>> - {[0 ... MAX_NUMNODES - 1] = NUMA_NO_NODE}; >>>> +#define DEFAULT_DEMOTION_TARGET_NODES 15 >>>> + >>>> +#if MAX_NUMNODES < DEFAULT_DEMOTION_TARGET_NODES >>>> +#define DEMOTION_TARGET_NODES (MAX_NUMNODES - 1) >>>> +#else >>>> +#define DEMOTION_TARGET_NODES DEFAULT_DEMOTION_TARGET_NODES >>>> +#endif >>>> + >>>> +struct demotion_nodes { >>>> + unsigned short nr; >>>> + short nodes[DEMOTION_TARGET_NODES]; >>>> +}; >>>> + >>>> +static struct demotion_nodes *node_demotion __read_mostly; >>>> >>>> /** >>>> * next_demotion_node() - Get the next node in the demotion path >>>> @@ -1149,8 +1175,15 @@ static int __unmap_and_move(struct page *page, struct page *newpage, >>>> */ >>>> int next_demotion_node(int node) >>>> { >>>> + struct demotion_nodes *nd; >>>> + unsigned short target_nr, index; >>>> int target; >>>> >>>> + if (!node_demotion) >>>> + return NUMA_NO_NODE; >>>> + >>>> + nd = &node_demotion[node]; >>>> + >>>> /* >>>> * node_demotion[] is updated without excluding this >>>> * function from running. RCU doesn't provide any >>>> @@ -1161,9 +1194,28 @@ int next_demotion_node(int node) >>>> * node_demotion[] reads need to be consistent. >>>> */ >>>> rcu_read_lock(); >>>> - target = READ_ONCE(node_demotion[node]); >>>> - rcu_read_unlock(); >>>> + target_nr = READ_ONCE(nd->nr); >>>> + >>>> + switch (target_nr) { >>>> + case 0: >>>> + target = NUMA_NO_NODE; >>>> + goto out; >>>> + case 1: >>>> + index = 0; >>>> + break; >>>> + default: >>>> + /* >>>> + * If there are multiple target nodes, just select one >>>> + * target node randomly. >>>> + */ >>>> + index = get_random_int() % target_nr; >>> >>> Sorry for chiming in late. I don't get why not select demotion targe > node interleave? TBH, it makes more sense to me. Random is ok, but at >>> least I'd expect to see some explanation about why random is used. >> >> My first version patch[1] already did round-robin to select target node. >> For interleave (or round-robin), we should introduce another member to >> record last selected target node, as Dave and Ying said, that will cause >> cache ping-pong to hurt performance, or introduce per-cpu data to avoid >> this, which seems more complicated now. > > Thanks. It should be better to have some words in the commit log or > code to elaborate this? Someone else may have the same question in the > future. OK. I saw Andrew has queued v4 patch, and I can create an incremental patch to add some comments to explain this. Thanks.