From nobody Thu Apr 9 12:06:26 2026 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 DE42EC433FE for ; Sat, 5 Nov 2022 01:40:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229588AbiKEBkd (ORCPT ); Fri, 4 Nov 2022 21:40:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35438 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229572AbiKEBk3 (ORCPT ); Fri, 4 Nov 2022 21:40:29 -0400 Received: from mail-pg1-x54a.google.com (mail-pg1-x54a.google.com [IPv6:2607:f8b0:4864:20::54a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0F78420193 for ; Fri, 4 Nov 2022 18:40:29 -0700 (PDT) Received: by mail-pg1-x54a.google.com with SMTP id f186-20020a636ac3000000b0044adaa7d347so3296512pgc.14 for ; Fri, 04 Nov 2022 18:40:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=8jkJGrxn/AkT1+zj9lg1NbIOC+/Y0zcaC/bhas2fS20=; b=sj1uClZYPWF9+g/Af6U4lnd/QJhXqeY3U+fGEwKz1MyD8aXjH0oZ0MZFjaSc6iuZLu zCdJYg8aA0oDVN58TmQ95Jm0SX7knr8iOICAk6In4Z3Zbb+Mz+b59VHuotsDCPKAf0OA j1gW8EYpt++wGl9NTi3NqMeFWAptSSYuZTEZsnKYNdAoVHRuLqoUY3sSQo+nDU61WdgA 5dwYUptpKy/a2PkcHkBhFsf/CujyPzLixs3RwqOEtbLanGANqZNoBnq9b3gE+iJq+hit eW+6YW19QOIUUELIv4oHvt54A5yWsRzqCEr78MVJU1wSdEWEHHdGSnkICTwkbiEo7SqX 6wcA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=8jkJGrxn/AkT1+zj9lg1NbIOC+/Y0zcaC/bhas2fS20=; b=wXBfHzNnofSWdpDznnS+ArJtq9BFfjbfxZgelZY6QAjbNSDAxoreV8+spc0w43xyzs f5RHxE3ggVzdfzGQfFNbE6bIVp58aHLb/YHInsgd9+txpXCvP61JN5GAUERJZ6JYOY/A WLF7w9FmKo3drFTK7mLqu0CtVTS5vHSx9vtxAWXh8fusQf0ClFHj92y6MGZgxEggHyi4 3XDzg3W2pSWaGMMMYbb7A0uLpj+s5JJO7pZl9QrYDEpi3vZoYhYV0icTJemzAJ13h5v0 j6kHbRMNZMk3iPBPygYy16Ib69YGEUvxxWeHmjPQcK9j6udOPJktRKS6mr0OubWlYiUI iD3w== X-Gm-Message-State: ANoB5pmcsY2EkP9V82lnQCTFF2hWMNgsNlvZ5T8c/V/05XkdlIbnQv06 9tdZKP3oOY5ZKE5wEe4tliqyfDrwAbIVmQ== X-Google-Smtp-Source: AA0mqf6jfoCQ+f91qDyQhm2aDDOkq+E3ZjTnt72QOCfo1bxzDsUFyW3esvQ31twA11J5QruAiX9io9bm22nHyA== X-Received: from shakeelb.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:262e]) (user=shakeelb job=sendgmr) by 2002:a17:90a:f291:b0:20a:eab5:cf39 with SMTP id fs17-20020a17090af29100b0020aeab5cf39mr99870pjb.1.1667612428036; Fri, 04 Nov 2022 18:40:28 -0700 (PDT) Date: Sat, 5 Nov 2022 01:40:13 +0000 Mime-Version: 1.0 X-Mailer: git-send-email 2.38.1.431.g37b22c650d-goog Message-ID: <20221105014013.930636-1-shakeelb@google.com> Subject: [PATCH] percpu_counter: add percpu_counter_sum_all interface From: Shakeel Butt To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Shakeel Butt , Marek Szyprowski Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The percpu_counter is used for scenarios where performance is more important than the accuracy. For percpu_counter users, who want more accurate information in their slowpath, percpu_counter_sum is provided which traverses all the online CPUs to accumulate the data. The reason it only needs to traverse online CPUs is because percpu_counter does implement CPU offline callback which syncs the local data of the offlined CPU. However there is a small race window between the online CPUs traversal of percpu_counter_sum and the CPU offline callback. The offline callback has to traverse all the percpu_counters on the system to flush the CPU local data which can be a lot. During that time, the CPU which is going offline has already been published as offline to all the readers. So, as the offline callback is running, percpu_counter_sum can be called for one counter which has some state on the CPU going offline. Since percpu_counter_sum only traverses online CPUs, it will skip that specific CPU and the offline callback might not have flushed the state for that specific percpu_counter on that offlined CPU. Normally this is not an issue because percpu_counter users can deal with some inaccuracy for small time window. However a new user i.e. mm_struct on the cleanup path wants to check the exact state of the percpu_counter through check_mm(). For such users, this patch introduces percpu_counter_sum_all() which traverses all possible CPUs. Signed-off-by: Shakeel Butt Reported-by: Marek Szyprowski Tested-by: Marek Szyprowski --- include/linux/percpu_counter.h | 6 ++++++ kernel/fork.c | 2 +- lib/percpu_counter.c | 29 +++++++++++++++++++++++------ 3 files changed, 30 insertions(+), 7 deletions(-) diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h index bde6c4c1f405..a3aae8d57a42 100644 --- a/include/linux/percpu_counter.h +++ b/include/linux/percpu_counter.h @@ -45,6 +45,7 @@ void percpu_counter_set(struct percpu_counter *fbc, s64 a= mount); void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch); s64 __percpu_counter_sum(struct percpu_counter *fbc); +s64 percpu_counter_sum_all(struct percpu_counter *fbc); int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batc= h); void percpu_counter_sync(struct percpu_counter *fbc); =20 @@ -193,6 +194,11 @@ static inline s64 percpu_counter_sum(struct percpu_cou= nter *fbc) return percpu_counter_read(fbc); } =20 +static inline s64 percpu_counter_sum_all(struct percpu_counter *fbc) +{ + return percpu_counter_read(fbc); +} + static inline bool percpu_counter_initialized(struct percpu_counter *fbc) { return true; diff --git a/kernel/fork.c b/kernel/fork.c index 9c32f593ef11..7d6f510cf397 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -756,7 +756,7 @@ static void check_mm(struct mm_struct *mm) "Please make sure 'struct resident_page_types[]' is updated as well"); =20 for (i =3D 0; i < NR_MM_COUNTERS; i++) { - long x =3D percpu_counter_sum(&mm->rss_stat[i]); + long x =3D percpu_counter_sum_all(&mm->rss_stat[i]); =20 if (unlikely(x)) pr_alert("BUG: Bad rss-counter state mm:%p type:%s val:%ld\n", diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c index ed610b75dc32..42f729c8e56c 100644 --- a/lib/percpu_counter.c +++ b/lib/percpu_counter.c @@ -117,11 +117,8 @@ void percpu_counter_sync(struct percpu_counter *fbc) } EXPORT_SYMBOL(percpu_counter_sync); =20 -/* - * Add up all the per-cpu counts, return the result. This is a more accur= ate - * but much slower version of percpu_counter_read_positive() - */ -s64 __percpu_counter_sum(struct percpu_counter *fbc) +static s64 __percpu_counter_sum_mask(struct percpu_counter *fbc, + const struct cpumask *cpu_mask) { s64 ret; int cpu; @@ -129,15 +126,35 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc) =20 raw_spin_lock_irqsave(&fbc->lock, flags); ret =3D fbc->count; - for_each_online_cpu(cpu) { + for_each_cpu(cpu, cpu_mask) { s32 *pcount =3D per_cpu_ptr(fbc->counters, cpu); ret +=3D *pcount; } raw_spin_unlock_irqrestore(&fbc->lock, flags); return ret; } + +/* + * Add up all the per-cpu counts, return the result. This is a more accur= ate + * but much slower version of percpu_counter_read_positive() + */ +s64 __percpu_counter_sum(struct percpu_counter *fbc) +{ + return __percpu_counter_sum_mask(fbc, cpu_online_mask); +} EXPORT_SYMBOL(__percpu_counter_sum); =20 +/* + * This is slower version of percpu_counter_sum as it traverses all possib= le + * cpus. Use this only in the cases where accurate data is needed in the + * presense of CPUs getting offlined. + */ +s64 percpu_counter_sum_all(struct percpu_counter *fbc) +{ + return __percpu_counter_sum_mask(fbc, cpu_possible_mask); +} +EXPORT_SYMBOL(percpu_counter_sum_all); + int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gf= p, struct lock_class_key *key) { --=20 2.38.1.431.g37b22c650d-goog