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=-6.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 72318C2BA1A for ; Tue, 7 Apr 2020 02:11:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4851E2076E for ; Tue, 7 Apr 2020 02:11:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="xI/ujC/R" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726504AbgDGCLV (ORCPT ); Mon, 6 Apr 2020 22:11:21 -0400 Received: from mail-qv1-f68.google.com ([209.85.219.68]:35595 "EHLO mail-qv1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726310AbgDGCLU (ORCPT ); Mon, 6 Apr 2020 22:11:20 -0400 Received: by mail-qv1-f68.google.com with SMTP id q73so1147603qvq.2 for ; Mon, 06 Apr 2020 19:11:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=aaa6SifOL9ZgGakR85u07GVO9twQQnlqkKhhw8LJ61Y=; b=xI/ujC/RAckrvStiyT1s/lKEcpA1186172WShsPNhGoEOvQ5y2Ser1kYDtJsnPsLga f6QPfBlDXJ4h7eLoL/ZFwg0+woBukzLR534NkFoPeELNS+GjxvNixkkD5xoEJUd4e+n9 Kyrm2zsmBCRaqyD3cOlNW7XK34Oqd7RmKL8vA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=aaa6SifOL9ZgGakR85u07GVO9twQQnlqkKhhw8LJ61Y=; b=Zja2vJokCuE5Rw4NkRoLlgGoPfNFfwJBZLYmvOwJoO7B8JgFCWljKoH5IpazoCRvzw w0UuH/cNE9OpeYhpL+oeUFRLdc3t81khwey4ZcM1NmmuY5XxcsMYNDEbet5J4k3PvS0o SMNZEDqF5phrqQi8klmrrl1C9bVYu+yiidwS0QKf7Sx/GJlM/EIeu2SEqwjHhoCleALv 4peK+jrymhuDFO3t3gcHjF48oCKQyeRrdd5xBXbt1D4Wn/i8CC+eM4V0OiNruwg1uJlp FIL9DqCn04hlmXvvdIjaIM0Hmf0wmBVLjO4WXSISyG72JpkbVss3K3X7vNzVSsfNvM2o AsEw== X-Gm-Message-State: AGi0Pub0vKvowlp8YktnM2LqC1Gpf2k2MOs2XhXDDdgDc4+4uTVlapkG //jcinUfBTeKK1eDDbfzgKwlag== X-Google-Smtp-Source: APiQypJXPpYd12Vrp+/OA+MjcYQlGqYJcYWnu164CU0oVIxQEvSPK9xJqC/qsXd3mxWCvZpUCgm1Ng== X-Received: by 2002:ad4:4f93:: with SMTP id em19mr84697qvb.110.1586225479431; Mon, 06 Apr 2020 19:11:19 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id g187sm15461721qkf.115.2020.04.06.19.11.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Apr 2020 19:11:18 -0700 (PDT) Date: Mon, 6 Apr 2020 22:11:18 -0400 From: Joel Fernandes To: "Uladzislau Rezki (Sony)" Cc: LKML , "Paul E . McKenney" , RCU , linux-mm@kvack.org, Andrew Morton , Steven Rostedt , Oleksiy Avramchenko Subject: Re: [PATCH 1/3] rcu/tree: use more permissive parameters when attaching a head Message-ID: <20200407021118.GB113967@google.com> References: <20200402123253.10382-1-urezki@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200402123253.10382-1-urezki@gmail.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 02, 2020 at 02:32:51PM +0200, Uladzislau Rezki (Sony) wrote: > It is documneted that a headless object can be reclaimed from > might_sleep() context only. Because of that when a head is > dynamically attached it makes sense to drop the lock and do > an allocation with much more permissve flags comparing if it > is done from atomic context. > > That is why use GFP_KERNEL flag plus some extra ones which > would make an allocation most likely to be succeed. The big > advantage of doing so is a direct reclaim process. > > Tested such approach on my local tiny system with 145MB of > ram(the minimum amount the KVM system is capable of booting) > and 4xCPUs. For stressing the rcuperf module was used. During > tests with difference combinations i did not observe any hit > of our last emergency case, when synchronize_rcu() is involved. > > Please note, the "dynamically attaching" path was enabled only, > apart of that all types of objects were considered as headless > variant during testing. > > Signed-off-by: Uladzislau Rezki (Sony) > Suggested-by: Joel Fernandes (Google) > --- > kernel/rcu/tree.c | 23 ++++++++++++++++------- > 1 file changed, 16 insertions(+), 7 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 6172e6296dd7..24f620a06219 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -3148,13 +3148,10 @@ static inline struct rcu_head *attach_rcu_head_to_object(void *obj) > { > unsigned long *ptr; > > + /* Try hard to get the memory. */ > ptr = kmalloc(sizeof(unsigned long *) + > - sizeof(struct rcu_head), GFP_NOWAIT | __GFP_NOWARN); > - > - if (!ptr) > - ptr = kmalloc(sizeof(unsigned long *) + > - sizeof(struct rcu_head), GFP_ATOMIC | __GFP_NOWARN); > - > + sizeof(struct rcu_head), GFP_KERNEL | > + __GFP_ATOMIC | __GFP_HIGH | __GFP_RETRY_MAYFAIL); On thing here though, you removed the NOWARN. Was there a reason? It would now warn even when synchronously waiting right? I will fixup your commit to add it back for now but let me know if you had some other reason to remove it. thanks, - Joel > if (!ptr) > return NULL; > > @@ -3222,9 +3219,20 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) > if (!success) { > /* Is headless object? */ > if (head == NULL) { > + /* Drop the lock. */ > + if (krcp->initialized) > + spin_unlock(&krcp->lock); > + local_irq_restore(flags); > + > head = attach_rcu_head_to_object(ptr); > if (head == NULL) > - goto unlock_return; > + goto inline_return; > + > + /* Take it back. */ > + local_irq_save(flags); > + krcp = this_cpu_ptr(&krc); > + if (krcp->initialized) > + spin_lock(&krcp->lock); > > /* > * Tag the headless object. Such objects have a back-pointer > @@ -3263,6 +3271,7 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) > spin_unlock(&krcp->lock); > local_irq_restore(flags); > > +inline_return: > /* > * High memory pressure, so inline kvfree() after > * synchronize_rcu(). We can do it from might_sleep() > -- > 2.20.1 >