From patchwork Fri Jun 24 12:54:21 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mel Gorman X-Patchwork-Id: 12894471 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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7E49AC43334 for ; Fri, 24 Jun 2022 12:55:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1C3E98E021B; Fri, 24 Jun 2022 08:55:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 126298E020E; Fri, 24 Jun 2022 08:55:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F0C4C8E021B; Fri, 24 Jun 2022 08:55:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id DE81D8E020E for ; Fri, 24 Jun 2022 08:55:29 -0400 (EDT) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id AF43E615EA for ; Fri, 24 Jun 2022 12:55:29 +0000 (UTC) X-FDA: 79613125578.30.A34BE41 Received: from outbound-smtp26.blacknight.com (outbound-smtp26.blacknight.com [81.17.249.194]) by imf05.hostedemail.com (Postfix) with ESMTP id 2AF3410002D for ; Fri, 24 Jun 2022 12:55:29 +0000 (UTC) Received: from mail.blacknight.com (pemlinmail06.blacknight.ie [81.17.255.152]) by outbound-smtp26.blacknight.com (Postfix) with ESMTPS id 1DF23CACC3 for ; Fri, 24 Jun 2022 13:55:28 +0100 (IST) Received: (qmail 8629 invoked from network); 24 Jun 2022 12:55:27 -0000 Received: from unknown (HELO morpheus.112glenside.lan) (mgorman@techsingularity.net@[84.203.198.246]) by 81.17.254.9 with ESMTPA; 24 Jun 2022 12:55:27 -0000 From: Mel Gorman To: Andrew Morton Cc: Nicolas Saenz Julienne , Marcelo Tosatti , Vlastimil Babka , Michal Hocko , Hugh Dickins , Yu Zhao , Marek Szyprowski , LKML , Linux-MM , Mel Gorman Subject: [PATCH 5/7] mm/page_alloc: Protect PCP lists with a spinlock Date: Fri, 24 Jun 2022 13:54:21 +0100 Message-Id: <20220624125423.6126-6-mgorman@techsingularity.net> X-Mailer: git-send-email 2.35.3 In-Reply-To: <20220624125423.6126-1-mgorman@techsingularity.net> References: <20220624125423.6126-1-mgorman@techsingularity.net> MIME-Version: 1.0 ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1656075329; a=rsa-sha256; cv=none; b=R5Q/CmF3sJ+uuyR70wbIobKYHheymZPD4d93qDJ6iumQdhpJGjLgu5odTrujWZ1mKR7qsr WllgTqu1j8KL05ZboQ2Ii9rlZenKiQanF/OUmSheHv4oGsdvjUF60tl5/FnpqE18LbVspy rsxzftCCCZCk3FynEGiLWpl2xcZa/HE= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf05.hostedemail.com: domain of mgorman@techsingularity.net designates 81.17.249.194 as permitted sender) smtp.mailfrom=mgorman@techsingularity.net ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1656075329; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=memmRGIqm9TajgTopA8Ggciz3jT0wK0xR/NDUtzsm/o=; b=69SUsH/PNC0uIiI+wC773sEELDc1HPnhB+6u+9soEpTCqGcdiUzkbwTHMH0jodZ595bCcS 7bsHi65jlmzh4AgsUEBp2kc31kesl/I/xE3vWn34qxzAYAOBIM7/2D5+MU/q7mDY9l8g1W +TovkYWGTevlP3qXqayFu6CCPe5fv+o= X-Stat-Signature: yauko85auyk9idyoszmizgojdrt3khgg X-Rspamd-Queue-Id: 2AF3410002D Authentication-Results: imf05.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf05.hostedemail.com: domain of mgorman@techsingularity.net designates 81.17.249.194 as permitted sender) smtp.mailfrom=mgorman@techsingularity.net X-Rspamd-Server: rspam10 X-Rspam-User: X-HE-Tag: 1656075329-717630 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: Currently the PCP lists are protected by using local_lock_irqsave to prevent migration and IRQ reentrancy but this is inconvenient. Remote draining of the lists is impossible and a workqueue is required and every task allocation/free must disable then enable interrupts which is expensive. As preparation for dealing with both of those problems, protect the lists with a spinlock. The IRQ-unsafe version of the lock is used because IRQs are already disabled by local_lock_irqsave. spin_trylock is used in preparation for a time when local_lock could be used instead of lock_lock_irqsave. The per_cpu_pages still fits within the same number of cache lines after this patch relative to before the series. struct per_cpu_pages { spinlock_t lock; /* 0 4 */ int count; /* 4 4 */ int high; /* 8 4 */ int batch; /* 12 4 */ short int free_factor; /* 16 2 */ short int expire; /* 18 2 */ /* XXX 4 bytes hole, try to pack */ struct list_head lists[13]; /* 24 208 */ /* size: 256, cachelines: 4, members: 7 */ /* sum members: 228, holes: 1, sum holes: 4 */ /* padding: 24 */ } __attribute__((__aligned__(64))); There is overhead in the fast path due to acquiring the spinlock even though the spinlock is per-cpu and uncontended in the common case. Page Fault Test (PFT) running on a 1-socket reported the following results on a 1 socket machine. 5.19.0-rc3 5.19.0-rc3 vanilla mm-pcpspinirq-v5r16 Hmean faults/sec-1 869275.7381 ( 0.00%) 874597.5167 * 0.61%* Hmean faults/sec-3 2370266.6681 ( 0.00%) 2379802.0362 * 0.40%* Hmean faults/sec-5 2701099.7019 ( 0.00%) 2664889.7003 * -1.34%* Hmean faults/sec-7 3517170.9157 ( 0.00%) 3491122.8242 * -0.74%* Hmean faults/sec-8 3965729.6187 ( 0.00%) 3939727.0243 * -0.66%* There is a small hit in the number of faults per second but given that the results are more stable, it's borderline noise. Signed-off-by: Mel Gorman Acked-by: Vlastimil Babka Reviewed-by: Nicolas Saenz Julienne Tested-by: Nicolas Saenz Julienne --- include/linux/mmzone.h | 1 + mm/page_alloc.c | 118 +++++++++++++++++++++++++++++++++-------- 2 files changed, 98 insertions(+), 21 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 4e0352cc2fcb..299259cfe462 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -382,6 +382,7 @@ enum zone_watermarks { /* Fields and list protected by pagesets local_lock in page_alloc.c */ struct per_cpu_pages { + spinlock_t lock; /* Protects lists field */ int count; /* number of pages in the list */ int high; /* high watermark, emptying needed */ int batch; /* chunk size for buddy add/remove */ diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 7fb262eeec2f..3b819c2720f8 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -133,6 +133,20 @@ static DEFINE_PER_CPU(struct pagesets, pagesets) = { .lock = INIT_LOCAL_LOCK(lock), }; +#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT) +/* + * On SMP, spin_trylock is sufficient protection. + * On PREEMPT_RT, spin_trylock is equivalent on both SMP and UP. + */ +#define pcp_trylock_prepare(flags) do { } while (0) +#define pcp_trylock_finish(flag) do { } while (0) +#else + +/* UP spin_trylock always succeeds so disable IRQs to prevent re-entrancy. */ +#define pcp_trylock_prepare(flags) local_irq_save(flags) +#define pcp_trylock_finish(flags) local_irq_restore(flags) +#endif + #ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID DEFINE_PER_CPU(int, numa_node); EXPORT_PER_CPU_SYMBOL(numa_node); @@ -3097,15 +3111,22 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order, */ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp) { - unsigned long flags; int to_drain, batch; - local_lock_irqsave(&pagesets.lock, flags); batch = READ_ONCE(pcp->batch); to_drain = min(pcp->count, batch); - if (to_drain > 0) + if (to_drain > 0) { + unsigned long flags; + + /* + * free_pcppages_bulk expects IRQs disabled for zone->lock + * so even though pcp->lock is not intended to be IRQ-safe, + * it's needed in this context. + */ + spin_lock_irqsave(&pcp->lock, flags); free_pcppages_bulk(zone, to_drain, pcp, 0); - local_unlock_irqrestore(&pagesets.lock, flags); + spin_unlock_irqrestore(&pcp->lock, flags); + } } #endif @@ -3118,16 +3139,17 @@ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp) */ static void drain_pages_zone(unsigned int cpu, struct zone *zone) { - unsigned long flags; struct per_cpu_pages *pcp; - local_lock_irqsave(&pagesets.lock, flags); - pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu); - if (pcp->count) - free_pcppages_bulk(zone, pcp->count, pcp, 0); + if (pcp->count) { + unsigned long flags; - local_unlock_irqrestore(&pagesets.lock, flags); + /* See drain_zone_pages on why this is disabling IRQs */ + spin_lock_irqsave(&pcp->lock, flags); + free_pcppages_bulk(zone, pcp->count, pcp, 0); + spin_unlock_irqrestore(&pcp->lock, flags); + } } /* @@ -3395,17 +3417,15 @@ static int nr_pcp_high(struct per_cpu_pages *pcp, struct zone *zone, return min(READ_ONCE(pcp->batch) << 2, high); } -static void free_unref_page_commit(struct page *page, int migratetype, +static void free_unref_page_commit(struct zone *zone, struct per_cpu_pages *pcp, + struct page *page, int migratetype, unsigned int order) { - struct zone *zone = page_zone(page); - struct per_cpu_pages *pcp; int high; int pindex; bool free_high; __count_vm_event(PGFREE); - pcp = this_cpu_ptr(zone->per_cpu_pageset); pindex = order_to_pindex(migratetype, order); list_add(&page->pcp_list, &pcp->lists[pindex]); pcp->count += 1 << order; @@ -3432,6 +3452,9 @@ static void free_unref_page_commit(struct page *page, int migratetype, void free_unref_page(struct page *page, unsigned int order) { unsigned long flags; + unsigned long __maybe_unused UP_flags; + struct per_cpu_pages *pcp; + struct zone *zone; unsigned long pfn = page_to_pfn(page); int migratetype; @@ -3455,7 +3478,16 @@ void free_unref_page(struct page *page, unsigned int order) } local_lock_irqsave(&pagesets.lock, flags); - free_unref_page_commit(page, migratetype, order); + zone = page_zone(page); + pcp_trylock_prepare(UP_flags); + pcp = this_cpu_ptr(zone->per_cpu_pageset); + if (spin_trylock(&pcp->lock)) { + free_unref_page_commit(zone, pcp, page, migratetype, order); + spin_unlock(&pcp->lock); + } else { + free_one_page(zone, page, pfn, order, migratetype, FPI_NONE); + } + pcp_trylock_finish(UP_flags); local_unlock_irqrestore(&pagesets.lock, flags); } @@ -3465,6 +3497,8 @@ void free_unref_page(struct page *page, unsigned int order) void free_unref_page_list(struct list_head *list) { struct page *page, *next; + struct per_cpu_pages *pcp = NULL; + struct zone *locked_zone = NULL; unsigned long flags; int batch_count = 0; int migratetype; @@ -3491,6 +3525,17 @@ void free_unref_page_list(struct list_head *list) local_lock_irqsave(&pagesets.lock, flags); list_for_each_entry_safe(page, next, list, lru) { + struct zone *zone = page_zone(page); + + /* Different zone, different pcp lock. */ + if (zone != locked_zone) { + if (pcp) + spin_unlock(&pcp->lock); + locked_zone = zone; + pcp = this_cpu_ptr(zone->per_cpu_pageset); + spin_lock(&pcp->lock); + } + /* * Non-isolated types over MIGRATE_PCPTYPES get added * to the MIGRATE_MOVABLE pcp list. @@ -3500,18 +3545,24 @@ void free_unref_page_list(struct list_head *list) migratetype = MIGRATE_MOVABLE; trace_mm_page_free_batched(page); - free_unref_page_commit(page, migratetype, 0); + free_unref_page_commit(zone, pcp, page, migratetype, 0); /* * Guard against excessive IRQ disabled times when we get * a large list of pages to free. */ if (++batch_count == SWAP_CLUSTER_MAX) { + spin_unlock(&pcp->lock); local_unlock_irqrestore(&pagesets.lock, flags); batch_count = 0; local_lock_irqsave(&pagesets.lock, flags); + pcp = this_cpu_ptr(locked_zone->per_cpu_pageset); + spin_lock(&pcp->lock); } } + + if (pcp) + spin_unlock(&pcp->lock); local_unlock_irqrestore(&pagesets.lock, flags); } @@ -3725,18 +3776,31 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone, struct list_head *list; struct page *page; unsigned long flags; + unsigned long __maybe_unused UP_flags; local_lock_irqsave(&pagesets.lock, flags); + /* + * spin_trylock may fail due to a parallel drain. In the future, the + * trylock will also protect against IRQ reentrancy. + */ + pcp = this_cpu_ptr(zone->per_cpu_pageset); + pcp_trylock_prepare(UP_flags); + if (!spin_trylock(&pcp->lock)) { + pcp_trylock_finish(UP_flags); + return NULL; + } + /* * On allocation, reduce the number of pages that are batch freed. * See nr_pcp_free() where free_factor is increased for subsequent * frees. */ - pcp = this_cpu_ptr(zone->per_cpu_pageset); pcp->free_factor >>= 1; list = &pcp->lists[order_to_pindex(migratetype, order)]; page = __rmqueue_pcplist(zone, order, migratetype, alloc_flags, pcp, list); + spin_unlock(&pcp->lock); + pcp_trylock_finish(UP_flags); local_unlock_irqrestore(&pagesets.lock, flags); if (page) { __count_zid_vm_events(PGALLOC, page_zonenum(page), 1); @@ -3771,7 +3835,8 @@ struct page *rmqueue(struct zone *preferred_zone, migratetype != MIGRATE_MOVABLE) { page = rmqueue_pcplist(preferred_zone, zone, order, gfp_flags, migratetype, alloc_flags); - goto out; + if (likely(page)) + goto out; } } @@ -5259,6 +5324,7 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid, { struct page *page; unsigned long flags; + unsigned long __maybe_unused UP_flags; struct zone *zone; struct zoneref *z; struct per_cpu_pages *pcp; @@ -5339,11 +5405,15 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid, if (unlikely(!zone)) goto failed; - /* Attempt the batch allocation */ + /* Is a parallel drain in progress? */ local_lock_irqsave(&pagesets.lock, flags); + pcp_trylock_prepare(UP_flags); pcp = this_cpu_ptr(zone->per_cpu_pageset); - pcp_list = &pcp->lists[order_to_pindex(ac.migratetype, 0)]; + if (!spin_trylock(&pcp->lock)) + goto failed_irq; + /* Attempt the batch allocation */ + pcp_list = &pcp->lists[order_to_pindex(ac.migratetype, 0)]; while (nr_populated < nr_pages) { /* Skip existing pages */ @@ -5356,8 +5426,10 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid, pcp, pcp_list); if (unlikely(!page)) { /* Try and allocate at least one page */ - if (!nr_account) + if (!nr_account) { + spin_unlock(&pcp->lock); goto failed_irq; + } break; } nr_account++; @@ -5370,6 +5442,8 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid, nr_populated++; } + spin_unlock(&pcp->lock); + pcp_trylock_finish(UP_flags); local_unlock_irqrestore(&pagesets.lock, flags); __count_zid_vm_events(PGALLOC, zone_idx(zone), nr_account); @@ -5379,6 +5453,7 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid, return nr_populated; failed_irq: + pcp_trylock_finish(UP_flags); local_unlock_irqrestore(&pagesets.lock, flags); failed: @@ -7019,6 +7094,7 @@ static void per_cpu_pages_init(struct per_cpu_pages *pcp, struct per_cpu_zonesta memset(pcp, 0, sizeof(*pcp)); memset(pzstats, 0, sizeof(*pzstats)); + spin_lock_init(&pcp->lock); for (pindex = 0; pindex < NR_PCP_LISTS; pindex++) INIT_LIST_HEAD(&pcp->lists[pindex]);