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=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 942F7FA372B for ; Wed, 16 Oct 2019 09:54:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 64E232168B for ; Wed, 16 Oct 2019 09:54:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="QE5ek4pV" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404369AbfJPJyv (ORCPT ); Wed, 16 Oct 2019 05:54:51 -0400 Received: from mail-lj1-f194.google.com ([209.85.208.194]:36463 "EHLO mail-lj1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728556AbfJPJyu (ORCPT ); Wed, 16 Oct 2019 05:54:50 -0400 Received: by mail-lj1-f194.google.com with SMTP id v24so23325230ljj.3 for ; Wed, 16 Oct 2019 02:54:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=bdoCE4EoxSLapTmXd4+oVGs4R70YFCwt9DjIODBWD6I=; b=QE5ek4pVPZfLzXJzV28P6nJ+0ySzes/vJ33aguYDmlDCotZp11VGmfub55bpIPwULu 445YzJByyi9BRAIfThepb5GU9gtU2sJw66rXQq2NXUn/K4dZOUAT1hnRMFbHniqB+JiG weY5ynwlgmCL0ItKNN1Ahe0Uxaw+QL7EQRIy+gWWoG2biYMDsmURA9GzkizOBx9Q5MAR GlB4hTBjI240TBfNo3FXNft53oV6xc4OyN+9u6a7TZYNCfNM55vYO4oSixwfV6A2LWAu ho2FLuaKimvVybjSGJRrV8X58Dg13nlrNVPA5wSaWe7KAy3j8b6QuhgnmpgQs7k4Bdn1 mP8g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=bdoCE4EoxSLapTmXd4+oVGs4R70YFCwt9DjIODBWD6I=; b=DDbEM/kahS1AIWRtHjVVfl/dyPMa+i6lo87HZKP2Nh1wqEkx9bB1kn+JJZ5v72cHG5 tTgjs8Ci19v/ZYC/a0/ZrvNfwIq7jvnkLbzg7vhy9a63faGyU8PuyhnU9Z3YxoU/kDJX HF39BOIurns0UkXVh9hTGhqhsy5Pf8o/m2Bxb2jaAp9+5mMXLDlCac7Wg+KHzLEjrh6K KxYoZqc2XPfR4sysTf/237Xa8+ywbtsqbSq6QXPkivXF6B47YW4P6abAR2DPm3ZV7Ix0 WceTBPz2ZwtGF8N+ch+H9XQncvPuS/bONWCH4O+0yBHwVcdV8Nure91KqFD8rSkDE6EK mxOg== X-Gm-Message-State: APjAAAWLdVYc4VcwcUQeOqB5xqrHNVMkZHSID/cczuDcV4aQEWIeImqu dlAO4x9fzMzYZNf75yfSqNM= X-Google-Smtp-Source: APXvYqxiDS53+QyM7r3Br5Xxnwu0u7VAzS+Uv9ERxHSO38DcMbzVXfh6Mfhp0Z22QaporVWAcWkmBQ== X-Received: by 2002:a2e:9d83:: with SMTP id c3mr25563346ljj.237.1571219688236; Wed, 16 Oct 2019 02:54:48 -0700 (PDT) Received: from pc636.semobile.internal ([37.139.158.167]) by smtp.gmail.com with ESMTPSA id b2sm886452lfq.27.2019.10.16.02.54.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Oct 2019 02:54:47 -0700 (PDT) From: "Uladzislau Rezki (Sony)" To: Andrew Morton Cc: Daniel Wagner , Sebastian Andrzej Siewior , Thomas Gleixner , linux-mm@kvack.org, LKML , Peter Zijlstra , Uladzislau Rezki , Hillf Danton , Michal Hocko , Matthew Wilcox , Oleksiy Avramchenko , Steven Rostedt Subject: [PATCH v3 1/3] mm/vmalloc: remove preempt_disable/enable when do preloading Date: Wed, 16 Oct 2019 11:54:36 +0200 Message-Id: <20191016095438.12391-1-urezki@gmail.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Some background. The preemption was disabled before to guarantee that a preloaded object is available for a CPU, it was stored for. The aim was to not allocate in atomic context when spinlock is taken later, for regular vmap allocations. But that approach conflicts with CONFIG_PREEMPT_RT philosophy. It means that calling spin_lock() with disabled preemption is forbidden in the CONFIG_PREEMPT_RT kernel. Therefore, get rid of preempt_disable() and preempt_enable() when the preload is done for splitting purpose. As a result we do not guarantee now that a CPU is preloaded, instead we minimize the case when it is not, with this change. For example i run the special test case that follows the preload pattern and path. 20 "unbind" threads run it and each does 1000000 allocations. Only 3.5 times among 1000000 a CPU was not preloaded. So it can happen but the number is negligible. V2 - > V3: - update the commit message V1 -> V2: - move __this_cpu_cmpxchg check when spin_lock is taken, as proposed by Andrew Morton - add more explanation in regard of preloading - adjust and move some comments Fixes: 82dd23e84be3 ("mm/vmalloc.c: preload a CPU with one object for split purpose") Reviewed-by: Steven Rostedt (VMware) Acked-by: Sebastian Andrzej Siewior Acked-by: Daniel Wagner Signed-off-by: Uladzislau Rezki (Sony) --- mm/vmalloc.c | 37 ++++++++++++++++++++----------------- 1 file changed, 20 insertions(+), 17 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index e92ff5f7dd8b..b7b443bfdd92 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -1078,31 +1078,34 @@ static struct vmap_area *alloc_vmap_area(unsigned long size, retry: /* - * Preload this CPU with one extra vmap_area object to ensure - * that we have it available when fit type of free area is - * NE_FIT_TYPE. + * Preload this CPU with one extra vmap_area object. It is used + * when fit type of free area is NE_FIT_TYPE. Please note, it + * does not guarantee that an allocation occurs on a CPU that + * is preloaded, instead we minimize the case when it is not. + * It can happen because of cpu migration, because there is a + * race until the below spinlock is taken. * * The preload is done in non-atomic context, thus it allows us * to use more permissive allocation masks to be more stable under - * low memory condition and high memory pressure. + * low memory condition and high memory pressure. In rare case, + * if not preloaded, GFP_NOWAIT is used. * - * Even if it fails we do not really care about that. Just proceed - * as it is. "overflow" path will refill the cache we allocate from. + * Set "pva" to NULL here, because of "retry" path. */ - preempt_disable(); - if (!__this_cpu_read(ne_fit_preload_node)) { - preempt_enable(); - pva = kmem_cache_alloc_node(vmap_area_cachep, GFP_KERNEL, node); - preempt_disable(); + pva = NULL; - if (__this_cpu_cmpxchg(ne_fit_preload_node, NULL, pva)) { - if (pva) - kmem_cache_free(vmap_area_cachep, pva); - } - } + if (!this_cpu_read(ne_fit_preload_node)) + /* + * Even if it fails we do not really care about that. + * Just proceed as it is. If needed "overflow" path + * will refill the cache we allocate from. + */ + pva = kmem_cache_alloc_node(vmap_area_cachep, GFP_KERNEL, node); spin_lock(&vmap_area_lock); - preempt_enable(); + + if (pva && __this_cpu_cmpxchg(ne_fit_preload_node, NULL, pva)) + kmem_cache_free(vmap_area_cachep, pva); /* * If an allocation fails, the "vend" address is -- 2.20.1