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=-6.6 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 DA860C433DF for ; Thu, 20 Aug 2020 21:57:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A5D722078D for ; Thu, 20 Aug 2020 21:57:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Lkupn2ml" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728257AbgHTV5j (ORCPT ); Thu, 20 Aug 2020 17:57:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59634 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726741AbgHTV5i (ORCPT ); Thu, 20 Aug 2020 17:57:38 -0400 Received: from mail-ed1-x541.google.com (mail-ed1-x541.google.com [IPv6:2a00:1450:4864:20::541]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 422F0C061385 for ; Thu, 20 Aug 2020 14:57:37 -0700 (PDT) Received: by mail-ed1-x541.google.com with SMTP id ba10so2858066edb.3 for ; Thu, 20 Aug 2020 14:57:37 -0700 (PDT) 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=5sviuv+X0eAsiZiEmZuhmbloJAvhEyc5WFuO1Rz+TUE=; b=Lkupn2ml+C7DdOtGP0lOruDZjCFfwnzZiuPeCknEHAgkiKMiLp80Ja6hMjPtqmGwRg TT8F0Wv4g0HogaPz3hrOrlrcVWXhd1IsuC5JePZNOf/kssSmniZdTvwFdRgaGt4YaZ0Q rFCWRB0OQPj4jKB7KQ6hJY+o7KyG/cTRE0A4+++Ykt6dzIeMPlNjBtQrsXICMScwq4PL j9LUtUltHPypHsbW0emiMMNTs0MTP1rQV21k+kiczIU+SB1vHp9kNDKV8/u23whPDOGK r4xKo/s2KKKV37pqz1MX9++vknCXJidYRfJ3BzYN2w4lmxL9z8PwNp2GBhxP3mRPmmjn TgtA== 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=5sviuv+X0eAsiZiEmZuhmbloJAvhEyc5WFuO1Rz+TUE=; b=AqP3siNIWENwhuZ3CVERzs1B62Z30BsSVSeQz62zuNcI57Z81AcmxbTkB45Lq3yoBE okUuy8OtYz64sUA0VpN5EO3y8WyoPGP8acbT+oN/qaqaCiisEcZbqk800ABA4FYUTNi/ ViM8xtRSzGHYdlyaIWI5YfcWqri4+On2eQ5fadWCobN2oxGmV3C2VuoXV5awCdLaB8lM EIl8zBZQbKxstuOnhhvJ0pHfPjyUBFNFGuO42x6964mSlqfCrkT68knisVrvPXDApYs1 A6p81aZWgdXoD4Lzfy1nhdgeytjJqcnYqVWHqKmfDX7Wo/8L2Rudpy6Go+jNjGpVSMFF Uvlg== X-Gm-Message-State: AOAM533nr6PgklqRwRUceCyDaK/a/XEkX8PkBwecvLlKaBby24/71AGZ GWM98xU5jss+PCcq0Gyn/TkmkmApkXXXRPY6aSA= X-Google-Smtp-Source: ABdhPJzKrnmPWoJ3402kaH5MO+iUdtgoRHgzZkmiw5vnRW2kpH0g12SVDvfqxXIyPzkglcjdj6Pwl4UAvV9zN8cfV3E= X-Received: by 2002:aa7:d983:: with SMTP id u3mr657139eds.366.1597960655895; Thu, 20 Aug 2020 14:57:35 -0700 (PDT) MIME-Version: 1.0 References: <20200818184122.29C415DF@viggo.jf.intel.com> <20200818184126.B8E91F10@viggo.jf.intel.com> In-Reply-To: <20200818184126.B8E91F10@viggo.jf.intel.com> From: Yang Shi Date: Thu, 20 Aug 2020 14:57:24 -0700 Message-ID: Subject: Re: [RFC][PATCH 2/9] mm/numa: automatically generate node migration order To: Dave Hansen Cc: Linux Kernel Mailing List , Yang Shi , David Rientjes , Huang Ying , Dan Williams Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 18, 2020 at 11:50 AM 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 > --- > > b/mm/internal.h | 1 > b/mm/migrate.c | 137 +++++++++++++++++++++++++++++++++++++++++++++++++++++- > b/mm/page_alloc.c | 2 > 3 files changed, 138 insertions(+), 2 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 2020-08-18 11:36:48.960583188 -0700 > +++ b/mm/internal.h 2020-08-18 11:36:48.968583188 -0700 > @@ -203,6 +203,7 @@ extern int user_min_free_kbytes; > > extern void zone_pcp_update(struct zone *zone); > extern void zone_pcp_reset(struct zone *zone); > +extern int find_next_best_node(int node, nodemask_t *used_node_mask); > > #if defined CONFIG_COMPACTION || defined CONFIG_CMA > > 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 2020-08-18 11:36:48.962583188 -0700 > +++ b/mm/migrate.c 2020-08-18 11:36:48.970583188 -0700 > @@ -1160,6 +1160,10 @@ out: > return rc; > } > > +/* > + * Writes to this array occur without locking. READ_ONCE() > + * is recommended for readers to ensure consistent reads. > + */ > static int node_demotion[MAX_NUMNODES] = {[0 ... MAX_NUMNODES - 1] = NUMA_NO_NODE}; > > /** > @@ -1173,7 +1177,13 @@ 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]); > } > > /* > @@ -3001,3 +3011,128 @@ 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. > + */ > +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(); Sounds better to move sp_wmb() into disable_all_migrate_targets()? I thought we need the barrier everytime disable_all_migrate_targets() is called, if so why not put them together to avoid overlooking? > + > + /* > + * 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 desintation. > + */ > + 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; > +} > + > +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 2020-08-18 11:36:48.964583188 -0700 > +++ b/mm/page_alloc.c 2020-08-18 11:36:48.972583188 -0700 > @@ -5607,7 +5607,7 @@ 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; > _