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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B9F2EC433EF for ; Fri, 24 Jun 2022 12:54:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231913AbiFXMyj (ORCPT ); Fri, 24 Jun 2022 08:54:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33686 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230053AbiFXMyi (ORCPT ); Fri, 24 Jun 2022 08:54:38 -0400 Received: from outbound-smtp11.blacknight.com (outbound-smtp11.blacknight.com [46.22.139.106]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A0816625A for ; Fri, 24 Jun 2022 05:54:36 -0700 (PDT) Received: from mail.blacknight.com (pemlinmail06.blacknight.ie [81.17.255.152]) by outbound-smtp11.blacknight.com (Postfix) with ESMTPS id 093D31C3BC0 for ; Fri, 24 Jun 2022 13:54:35 +0100 (IST) Received: (qmail 6834 invoked from network); 24 Jun 2022 12:54:34 -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 12:54:34 -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 v5 00/7] Drain remote per-cpu directly Date: Fri, 24 Jun 2022 13:54:16 +0100 Message-Id: <20220624125423.6126-1-mgorman@techsingularity.net> X-Mailer: git-send-email 2.35.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This replaces the existing version on mm-unstable. While there are some fixes, this is mostly refactoring of patch 5 based on Vlastimil's feedback to reduce churn in later patches. The level of refactoring made -fix patches excessively complicated. Changelog since v4 o Fix lockdep issues in patch 7 o Refactor patch 5 to reduce churn in patches 6 and 7 o Rebase to 5.19-rc3 Some setups, notably NOHZ_FULL CPUs, may be running realtime or latency-sensitive applications that cannot tolerate interference due to per-cpu drain work queued by __drain_all_pages(). Introduce a new mechanism to remotely drain the per-cpu lists. It is made possible by remotely locking 'struct per_cpu_pages' new per-cpu spinlocks. This has two advantages, the time to drain is more predictable and other unrelated tasks are not interrupted. This series has the same intent as Nicolas' series "mm/page_alloc: Remote per-cpu lists drain support" -- avoid interference of a high priority task due to a workqueue item draining per-cpu page lists. While many workloads can tolerate a brief interruption, it may cause a real-time task running on a NOHZ_FULL CPU to miss a deadline and at minimum, the draining is non-deterministic. Currently an IRQ-safe local_lock protects the page allocator per-cpu lists. The local_lock on its own prevents migration and the IRQ disabling protects from corruption due to an interrupt arriving while a page allocation is in progress. This series adjusts the locking. A spinlock is added to struct per_cpu_pages to protect the list contents while local_lock_irq is ultimately replaced by just the spinlock in the final patch. This allows a remote CPU to safely. Follow-on work should allow the spin_lock_irqsave to be converted to spin_lock to avoid IRQs being disabled/enabled in most cases. The follow-on patch will be one kernel release later as it is relatively high risk and it'll make bisections more clear if there are any problems. Patch 1 is a cosmetic patch to clarify when page->lru is storing buddy pages and when it is storing per-cpu pages. Patch 2 shrinks per_cpu_pages to make room for a spin lock. Strictly speaking this is not necessary but it avoids per_cpu_pages consuming another cache line. Patch 3 is a preparation patch to avoid code duplication. Patch 4 is a minor correction. Patch 5 uses a spin_lock to protect the per_cpu_pages contents while still relying on local_lock to prevent migration, stabilise the pcp lookup and prevent IRQ reentrancy. Patch 6 remote drains per-cpu pages directly instead of using a workqueue. Patch 7 uses a normal spinlock instead of local_lock for remote draining Nicolas Saenz Julienne (1): mm/page_alloc: Remotely drain per-cpu lists include/linux/mm_types.h | 5 + include/linux/mmzone.h | 12 +- mm/page_alloc.c | 386 ++++++++++++++++++++++++--------------- 3 files changed, 250 insertions(+), 153 deletions(-) -- 2.35.3