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 X-Spam-Level: X-Spam-Status: No, score=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 27D40C433DB for ; Mon, 8 Mar 2021 23:59:56 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A17D86528A for ; Mon, 8 Mar 2021 23:59:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A17D86528A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 3A3988D008D; Mon, 8 Mar 2021 18:59:55 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 355AD8D007F; Mon, 8 Mar 2021 18:59:55 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1A68D8D008D; Mon, 8 Mar 2021 18:59:55 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0072.hostedemail.com [216.40.44.72]) by kanga.kvack.org (Postfix) with ESMTP id EEC068D007F for ; Mon, 8 Mar 2021 18:59:54 -0500 (EST) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id B6DAF2C8B for ; Mon, 8 Mar 2021 23:59:54 +0000 (UTC) X-FDA: 77898377508.11.F6EE35C Received: from mail-ej1-f48.google.com (mail-ej1-f48.google.com [209.85.218.48]) by imf03.hostedemail.com (Postfix) with ESMTP id 4DA59C0007C8 for ; Mon, 8 Mar 2021 23:59:52 +0000 (UTC) Received: by mail-ej1-f48.google.com with SMTP id c10so23886754ejx.9 for ; Mon, 08 Mar 2021 15:59:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=VNvsfKjrGHPvBA7Usji3iBuG0BWPUzNjKszDD0Y16Dw=; b=L+fcis0fotbKgTcXw6qhudVFNwO2M+uI03ENlcTAr4A70wzeJhbfXA2wffMayiQXtv tLXQy8zsWozgEKftk9Of6Z9EYwLFZaq52pH65MB8C8Q0U2OzcPbwJwCyf3j94OFtprC7 TvwU2lg0XyMIREAUUy7twstZW4kvDdsQ/TWnNe+s4gUzj+V5WvOhEI8P6qKLJWaS4F3j mC/6KU4syh50fRbizo3HPqeNAp2srKizV32dKKBqrh36VY8FF3kxx8rKhMCLWHhYJpyS aBjgfFyewmoEvtzzOgx+Cpzg9IybNS3xRHRQqFNt2L8wOu+dAT6l03OUD8Mzsx5j+JcU qOlw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=VNvsfKjrGHPvBA7Usji3iBuG0BWPUzNjKszDD0Y16Dw=; b=H2zWeXardN+l+/wN2hCL7GGbPy1BXUI26t1QIguJOXWzMXmRW1pdogP1tPud2K+se6 AYRg9WSe/BoE7A/DdFRuVe3DDHWroZEZ8fajFNyv74PhL+eujRl02MuZiHhgug3lPaCT wdACDB4zyp2TzKEHeX46sU7pvmUmeWyQbKeUtLcG62yUSt/0gM2JiYnECxiJ9hNXLRl9 5gHCGjkeyrU+GBgrPWIYttheYUihDqNMyoRjeAU962PoKIFH0RRerUZmK1gQGGkV/4CF ZHIa3qoORAEfW+FJEQMZG/u4iG2DGuUC+h0fVDscXxHfq2wPoZwsOm4/d1JxUlVaiEmz K9xA== X-Gm-Message-State: AOAM531ejJ9ReE3SH0c7E6mrNVnjzXhxcnEgcxympZTe1RdA+h5JqxsT V2W/jfhnkPvj/nQ2BBtj/tjgjzVhSG0fhTxU/3Q= X-Google-Smtp-Source: ABdhPJyBD3mApp1a/jp+NcyCV67/HL1GaHQDJiqUFtI71100B5rwVnStJZY1AsfbisYzvTKqrlEJrt90mCE7bw6ZolU= X-Received: by 2002:a17:906:3088:: with SMTP id 8mr17156549ejv.499.1615247993195; Mon, 08 Mar 2021 15:59:53 -0800 (PST) MIME-Version: 1.0 References: <20210304235949.7922C1C3@viggo.jf.intel.com> <20210304235952.15D0CD27@viggo.jf.intel.com> In-Reply-To: <20210304235952.15D0CD27@viggo.jf.intel.com> From: Yang Shi Date: Mon, 8 Mar 2021 15:59:41 -0800 Message-ID: Subject: Re: [PATCH 02/10] mm/numa: automatically generate node migration order To: Dave Hansen Cc: Linux Kernel Mailing List , Linux MM , Yang Shi , David Rientjes , Huang Ying , Dan Williams , David Hildenbrand , Oscar Salvador Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4DA59C0007C8 X-Stat-Signature: cdnjkh6fu8n4b74xyxhzry8tp69fqsi7 Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf03; identity=mailfrom; envelope-from=""; helo=mail-ej1-f48.google.com; client-ip=209.85.218.48 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615247992-276978 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Mar 4, 2021 at 4:00 PM Dave Hansen wrote: > > > From: Dave Hansen > > When memory fills up on a node, memory contents can be > automatically migrated to another node. The biggest problems are > knowing when to migrate and to where the migration should be > targeted. > > The most straightforward way to generate the "to where" list > would be to follow the page allocator fallback lists. Those > lists already tell us if memory is full where to look next. It > would also be logical to move memory in that order. > > But, the allocator fallback lists have a fatal flaw: most nodes > appear in all the lists. This would potentially lead to > migration cycles (A->B, B->A, A->B, ...). > > Instead of using the allocator fallback lists directly, keep a > separate node migration ordering. But, reuse the same data used > to generate page allocator fallback in the first place: > find_next_best_node(). > > This means that the firmware data used to populate node distances > essentially dictates the ordering for now. It should also be > architecture-neutral since all NUMA architectures have a working > find_next_best_node(). > > The protocol for node_demotion[] access and writing is not > standard. It has no specific locking and is intended to be read > locklessly. Readers must take care to avoid observing changes > that appear incoherent. This was done so that node_demotion[] > locking has no chance of becoming a bottleneck on large systems > with lots of CPUs in direct reclaim. > > This code is unused for now. It will be called later in the > series. > > Signed-off-by: Dave Hansen > Cc: Yang Shi > Cc: David Rientjes > Cc: Huang Ying > Cc: Dan Williams > Cc: David Hildenbrand > Cc: osalvador > > -- > > changes from 20200122: > * Add big node_demotion[] comment Thanks for adding the comment. Reviewed-by: Yang Shi > --- > > b/mm/internal.h | 5 + > b/mm/migrate.c | 174 +++++++++++++++++++++++++++++++++++++++++++++++++++++- > b/mm/page_alloc.c | 4 - > 3 files changed, 180 insertions(+), 3 deletions(-) > > diff -puN mm/internal.h~auto-setup-default-migration-path-from-firmware mm/internal.h > --- a/mm/internal.h~auto-setup-default-migration-path-from-firmware 2021-03-04 15:35:52.407806439 -0800 > +++ b/mm/internal.h 2021-03-04 15:35:52.426806439 -0800 > @@ -520,12 +520,17 @@ static inline void mminit_validate_memmo > > #ifdef CONFIG_NUMA > extern int node_reclaim(struct pglist_data *, gfp_t, unsigned int); > +extern int find_next_best_node(int node, nodemask_t *used_node_mask); > #else > static inline int node_reclaim(struct pglist_data *pgdat, gfp_t mask, > unsigned int order) > { > return NODE_RECLAIM_NOSCAN; > } > +static inline int find_next_best_node(int node, nodemask_t *used_node_mask) > +{ > + return NUMA_NO_NODE; > +} > #endif > > extern int hwpoison_filter(struct page *p); > diff -puN mm/migrate.c~auto-setup-default-migration-path-from-firmware mm/migrate.c > --- a/mm/migrate.c~auto-setup-default-migration-path-from-firmware 2021-03-04 15:35:52.409806439 -0800 > +++ b/mm/migrate.c 2021-03-04 15:35:52.427806439 -0800 > @@ -1157,6 +1157,44 @@ out: > return rc; > } > > + > +/* > + * node_demotion[] example: > + * > + * Consider a system with two sockets. Each socket has > + * three classes of memory attached: fast, medium and slow. > + * Each memory class is placed in its own NUMA node. The > + * CPUs are placed in the node with the "fast" memory. The > + * 6 NUMA nodes (0-5) might be split among the sockets like > + * this: > + * > + * Socket A: 0, 1, 2 > + * Socket B: 3, 4, 5 > + * > + * When Node 0 fills up, its memory should be migrated to > + * Node 1. When Node 1 fills up, it should be migrated to > + * Node 2. The migration path start on the nodes with the > + * processors (since allocations default to this node) and > + * fast memory, progress through medium and end with the > + * slow memory: > + * > + * 0 -> 1 -> 2 -> stop > + * 3 -> 4 -> 5 -> stop > + * > + * 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 1 > + * 5, // Node 4 migrates to 2 > + * -1} // Node 5 does not migrate > + */ > + > +/* > + * Writes to this array occur without locking. READ_ONCE() > + * is recommended for readers to ensure consistent reads. > + */ > static int node_demotion[MAX_NUMNODES] __read_mostly = > {[0 ... MAX_NUMNODES - 1] = NUMA_NO_NODE}; > > @@ -1171,7 +1209,13 @@ static int node_demotion[MAX_NUMNODES] _ > */ > int next_demotion_node(int node) > { > - return node_demotion[node]; > + /* > + * node_demotion[] is updated without excluding > + * this function from running. READ_ONCE() avoids > + * reading multiple, inconsistent 'node' values > + * during an update. > + */ > + return READ_ONCE(node_demotion[node]); > } > > /* > @@ -3175,3 +3219,131 @@ void migrate_vma_finalize(struct migrate > } > EXPORT_SYMBOL(migrate_vma_finalize); > #endif /* CONFIG_DEVICE_PRIVATE */ > + > +/* Disable reclaim-based migration. */ > +static void disable_all_migrate_targets(void) > +{ > + int node; > + > + for_each_online_node(node) > + node_demotion[node] = NUMA_NO_NODE; > +} > + > +/* > + * Find an automatic demotion target for 'node'. > + * Failing here is OK. It might just indicate > + * being at the end of a chain. > + */ > +static int establish_migrate_target(int node, nodemask_t *used) > +{ > + int migration_target; > + > + /* > + * Can not set a migration target on a > + * node with it already set. > + * > + * No need for READ_ONCE() here since this > + * in the write path for node_demotion[]. > + * This should be the only thread writing. > + */ > + if (node_demotion[node] != NUMA_NO_NODE) > + return NUMA_NO_NODE; > + > + migration_target = find_next_best_node(node, used); > + if (migration_target == NUMA_NO_NODE) > + return NUMA_NO_NODE; > + > + node_demotion[node] = migration_target; > + > + return migration_target; > +} > + > +/* > + * When memory fills up on a node, memory contents can be > + * automatically migrated to another node instead of > + * discarded at reclaim. > + * > + * Establish a "migration path" which will start at nodes > + * with CPUs and will follow the priorities used to build the > + * page allocator zonelists. > + * > + * The difference here is that cycles must be avoided. If > + * node0 migrates to node1, then neither node1, nor anything > + * node1 migrates to can migrate to node0. > + * > + * This function can run simultaneously with readers of > + * node_demotion[]. However, it can not run simultaneously > + * with itself. Exclusion is provided by memory hotplug events > + * being single-threaded. > + */ > +static void __set_migration_target_nodes(void) > +{ > + nodemask_t next_pass = NODE_MASK_NONE; > + nodemask_t this_pass = NODE_MASK_NONE; > + nodemask_t used_targets = NODE_MASK_NONE; > + int node; > + > + /* > + * Avoid any oddities like cycles that could occur > + * from changes in the topology. This will leave > + * a momentary gap when migration is disabled. > + */ > + disable_all_migrate_targets(); > + > + /* > + * Ensure that the "disable" is visible across the system. > + * Readers will see either a combination of before+disable > + * state or disable+after. They will never see before and > + * after state together. > + * > + * The before+after state together might have cycles and > + * could cause readers to do things like loop until this > + * function finishes. This ensures they can only see a > + * single "bad" read and would, for instance, only loop > + * once. > + */ > + smp_wmb(); > + > + /* > + * Allocations go close to CPUs, first. Assume that > + * the migration path starts at the nodes with CPUs. > + */ > + next_pass = node_states[N_CPU]; > +again: > + this_pass = next_pass; > + next_pass = NODE_MASK_NONE; > + /* > + * To avoid cycles in the migration "graph", ensure > + * that migration sources are not future targets by > + * setting them in 'used_targets'. Do this only > + * once per pass so that multiple source nodes can > + * share a target node. > + * > + * 'used_targets' will become unavailable in future > + * passes. This limits some opportunities for > + * multiple source nodes to share a destination. > + */ > + nodes_or(used_targets, used_targets, this_pass); > + for_each_node_mask(node, this_pass) { > + int target_node = establish_migrate_target(node, &used_targets); > + > + if (target_node == NUMA_NO_NODE) > + continue; > + > + /* Visit targets from this pass in the next pass: */ > + node_set(target_node, next_pass); > + } > + /* Is another pass necessary? */ > + if (!nodes_empty(next_pass)) > + goto again; > +} > + > +/* > + * For callers that do not hold get_online_mems() already. > + */ > +static void set_migration_target_nodes(void) > +{ > + get_online_mems(); > + __set_migration_target_nodes(); > + put_online_mems(); > +} > diff -puN mm/page_alloc.c~auto-setup-default-migration-path-from-firmware mm/page_alloc.c > --- a/mm/page_alloc.c~auto-setup-default-migration-path-from-firmware 2021-03-04 15:35:52.422806439 -0800 > +++ b/mm/page_alloc.c 2021-03-04 15:35:52.429806439 -0800 > @@ -3916,7 +3916,7 @@ retry: > if (alloc_flags & ALLOC_NO_WATERMARKS) > goto try_this_zone; > > - if (!node_reclaim_enabled() || > + if (node_reclaim_mode == 0 || > !zone_allows_reclaim(ac->preferred_zoneref->zone, zone)) > continue; > > @@ -5773,7 +5773,7 @@ static int node_load[MAX_NUMNODES]; > * > * Return: node id of the found node or %NUMA_NO_NODE if no node is found. > */ > -static int find_next_best_node(int node, nodemask_t *used_node_mask) > +int find_next_best_node(int node, nodemask_t *used_node_mask) > { > int n, val; > int min_val = INT_MAX; > _ >