From mboxrd@z Thu Jan 1 00:00:00 1970 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 9B758C433F5 for ; Sun, 14 Nov 2021 14:40:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 80CCB60EFD for ; Sun, 14 Nov 2021 14:40:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232759AbhKNOm4 (ORCPT ); Sun, 14 Nov 2021 09:42:56 -0500 Received: from out30-54.freemail.mail.aliyun.com ([115.124.30.54]:50822 "EHLO out30-54.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229563AbhKNOmp (ORCPT ); Sun, 14 Nov 2021 09:42:45 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04357;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0UwSyb1p_1636900788; Received: from 192.168.0.103(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0UwSyb1p_1636900788) by smtp.aliyun-inc.com(127.0.0.1); Sun, 14 Nov 2021 22:39:49 +0800 Message-ID: Date: Sun, 14 Nov 2021 22:40:35 +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 2021/11/13 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. [1] https://lore.kernel.org/all/c02bcbc04faa7a2c852534e9cd58a91c44494657.1636016609.git.baolin.wang@linux.alibaba.com/