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 661FEC001DF for ; Wed, 2 Aug 2023 15:58:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235492AbjHBP6w (ORCPT ); Wed, 2 Aug 2023 11:58:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47500 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235495AbjHBP6i (ORCPT ); Wed, 2 Aug 2023 11:58:38 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0A8CF2103; Wed, 2 Aug 2023 08:58:35 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 69FBF61A10; Wed, 2 Aug 2023 15:58:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B69DCC433C9; Wed, 2 Aug 2023 15:58:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1690991913; bh=9xubLaIO5MdhpiaxNsf8DSgID/M5lEj2ExNCYUJF2Ts=; h=Date:To:From:Subject:From; b=Rz4avHmrVNYWJxVZNqJRmoEgYG8wpCz/AOIWNLGQ1kHuKAaljYsF/1rMw52jwZQYx /fbqD+O4cgvLmEgYvnkWfAgG6UlWpjXiY4UGBgrGwdfMUNRnNd5Y4p6HYC+qfe1439 6SeCYFWlf5G3d0Oxa7auWTHW5BHjf8z0KwEW6ro8= Date: Wed, 02 Aug 2023 08:58:33 -0700 To: mm-commits@vger.kernel.org, zhengqi.arch@bytedance.com, yuzhao@google.com, surenb@google.com, suleiman@google.com, steven@liquorix.net, stable@vger.kernel.org, quic_charante@quicinc.com, oleksandr@natalenko.name, matthias.bgg@gmail.com, lecopzer.chen@mediatek.com, heftig@archlinux.org, bgeffon@google.com, baohua@kernel.org, angelogioacchino.delregno@collabora.com, aneesh.kumar@linux.ibm.com, kaleshsingh@google.com, akpm@linux-foundation.org From: Andrew Morton Subject: + mm-unstable-multi-gen-lru-avoid-race-in-inc_min_seq.patch added to mm-unstable branch Message-Id: <20230802155833.B69DCC433C9@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The patch titled Subject: Multi-gen LRU: Avoid race in inc_min_seq() has been added to the -mm mm-unstable branch. Its filename is mm-unstable-multi-gen-lru-avoid-race-in-inc_min_seq.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-unstable-multi-gen-lru-avoid-race-in-inc_min_seq.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Kalesh Singh Subject: Multi-gen LRU: Avoid race in inc_min_seq() Date: Tue, 1 Aug 2023 19:56:03 -0700 inc_max_seq() will try to inc_min_seq() if nr_gens == MAX_NR_GENS. This is because the generations are reused (the last oldest now empty generation will become the next youngest generation). inc_min_seq() is retried until successful, dropping the lru_lock and yielding the CPU on each failure, and retaking the lock before trying again: while (!inc_min_seq(lruvec, type, can_swap)) { spin_unlock_irq(&lruvec->lru_lock); cond_resched(); spin_lock_irq(&lruvec->lru_lock); } However, the initial condition that required incrementing the min_seq (nr_gens == MAX_NR_GENS) is not retested. This can change by another call to inc_max_seq() from run_aging() with force_scan=true from the debugfs interface. Since the eviction stalls when the nr_gens == MIN_NR_GENS, avoid unnecessarily incrementing the min_seq by rechecking the number of generations before each attempt. This issue was uncovered in previous discussion on the list by Yu Zhao and Aneesh Kumar [1]. [1] https://lore.kernel.org/linux-mm/CAOUHufbO7CaVm=xjEb1avDhHVvnC8pJmGyKcFf2iY_dpf+zR3w@mail.gmail.com/ Link: https://lkml.kernel.org/r/20230802025606.346758-2-kaleshsingh@google.com Fixes: d6c3af7d8a2b ("mm: multi-gen LRU: debugfs interface") Signed-off-by: Kalesh Singh Tested-by: AngeloGioacchino Del Regno [mediatek] Tested-by: Charan Teja Kalla Cc: Yu Zhao Cc: Aneesh Kumar K V Cc: Barry Song Cc: Brian Geffon Cc: Jan Alexander Steffens (heftig) Cc: Lecopzer Chen Cc: Matthias Brugger Cc: Oleksandr Natalenko Cc: Qi Zheng Cc: Steven Barrett Cc: Suleiman Souhlal Cc: Suren Baghdasaryan Cc: Signed-off-by: Andrew Morton --- mm/vmscan.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) --- a/mm/vmscan.c~mm-unstable-multi-gen-lru-avoid-race-in-inc_min_seq +++ a/mm/vmscan.c @@ -4439,7 +4439,7 @@ static void inc_max_seq(struct lruvec *l int prev, next; int type, zone; struct lru_gen_folio *lrugen = &lruvec->lrugen; - +restart: spin_lock_irq(&lruvec->lru_lock); VM_WARN_ON_ONCE(!seq_is_valid(lruvec)); @@ -4450,11 +4450,12 @@ static void inc_max_seq(struct lruvec *l VM_WARN_ON_ONCE(!force_scan && (type == LRU_GEN_FILE || can_swap)); - while (!inc_min_seq(lruvec, type, can_swap)) { - spin_unlock_irq(&lruvec->lru_lock); - cond_resched(); - spin_lock_irq(&lruvec->lru_lock); - } + if (inc_min_seq(lruvec, type, can_swap)) + continue; + + spin_unlock_irq(&lruvec->lru_lock); + cond_resched(); + goto restart; } /* _ Patches currently in -mm which might be from kaleshsingh@google.com are mm-unstable-multi-gen-lru-fix-per-zone-reclaim.patch mm-unstable-multi-gen-lru-avoid-race-in-inc_min_seq.patch mm-unstable-multi-gen-lru-fix-can_swap-in-lru_gen_look_around.patch