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=-13.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 CBAF1C2D0F2 for ; Tue, 31 Mar 2020 14:58:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9FAF12078B for ; Tue, 31 Mar 2020 14:58:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="kX2+YjEF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730851AbgCaO6J (ORCPT ); Tue, 31 Mar 2020 10:58:09 -0400 Received: from mail-qk1-f195.google.com ([209.85.222.195]:44409 "EHLO mail-qk1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730592AbgCaO6J (ORCPT ); Tue, 31 Mar 2020 10:58:09 -0400 Received: by mail-qk1-f195.google.com with SMTP id j4so23223395qkc.11 for ; Tue, 31 Mar 2020 07:58:08 -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:user-agent; bh=cIZTwSTovCqpZjcH+8VKON/BYcVXt4dyLFHN/7fWLC0=; b=kX2+YjEFA7reVl0nZqgetW7HHWs3WBI8tDuovxTjTwwVwqW3601QSEjGEsCGuePVj7 LeJYnQq9IpkrFubdFv7FGPJwARcYAe9R6jylxk3Pa+7d/tXkyxj20UwItvKvKi6iEgdm 3Bb9hGRRxwfEbpNgz5aR7L0gIR2HceLIlhu8U= 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:user-agent; bh=cIZTwSTovCqpZjcH+8VKON/BYcVXt4dyLFHN/7fWLC0=; b=MIhaCWOPiG9Wk4Trdg5qkMaK6tfglwf6PO8i6B4ML9wCteAP8OYjVr2RBoc+nZrhTs DlsQYqSvLXHYu4mcY5oLY6zz8YSHTI6YM2p8LPOW7PGjQU6Gq9979THRzVjYvwJGkg9F 8INb77KJiKGOj/L/VhQS/nJD0HZHLOPYxpT55piEpMMGQu67I6e1SowZD93fN9r4iD03 linI4463Jpk1LYsdAzDl55RRueOcUlBUD/AzIZG0u+bguqSKMdj1hrwgjxTkLMwyEtHB QluCxQFkO5aV1Xw7VMkiWg+CakHuAYK+6iSaihYOZM0zUpPOcvyyAUNYMkZpXRp/UTqN INFw== X-Gm-Message-State: ANhLgQ2QRFH2ph0R+NVYaCxQyOYu0DU+cacNCTJfEbo/dYz1F2Uvn4Xt hfzm2j18Na8e4lQ0zQqNAs+tAtxytwE= X-Google-Smtp-Source: ADFU+vvPtFUJr9gLEzw5E54meLVFZylfDHn2cwkCKpLYfEDzB9hmFVGY0wKdA27LYbe+/zml0iNEug== X-Received: by 2002:a37:a4d6:: with SMTP id n205mr5467313qke.352.1585666687349; Tue, 31 Mar 2020 07:58:07 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id n142sm12693714qkn.11.2020.03.31.07.58.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Mar 2020 07:58:06 -0700 (PDT) Date: Tue, 31 Mar 2020 10:58:06 -0400 From: Joel Fernandes To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, rcu@vger.kernel.org, willy@infradead.org, peterz@infradead.org, neilb@suse.com, vbabka@suse.cz, mgorman@suse.de, Andrew Morton , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , "Paul E. McKenney" , Steven Rostedt Subject: Re: [PATCH RFC] rcu/tree: Use GFP_MEMALLOC for alloc memory to free memory pattern Message-ID: <20200331145806.GB236678@google.com> References: <20200331131628.153118-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200331131628.153118-1-joel@joelfernandes.org> User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 31, 2020 at 09:16:28AM -0400, Joel Fernandes (Google) wrote: > In kfree_rcu() headless implementation (where the caller need not pass > an rcu_head, but rather directly pass a pointer to an object), we have > a fall-back where we allocate a rcu_head wrapper for the caller (not the > common case). This brings the pattern of needing to allocate some memory > to free some memory. Currently we use GFP_ATOMIC flag to try harder for > this allocation, however the GFP_MEMALLOC flag is more tailored to this > pattern. We need to try harder not only during atomic context, but also > during non-atomic context anyway. So use the GFP_MEMALLOC flag instead. > > Also remove the __GFP_NOWARN flag simply because although we do have a > synchronize_rcu() fallback for absolutely worst case, we still would > like to not enter that path and atleast trigger a warning to the user. > > Cc: linux-mm@kvack.org > Cc: rcu@vger.kernel.org > Cc: willy@infradead.org > Cc: peterz@infradead.org > Cc: neilb@suse.com > Cc: vbabka@suse.cz > Cc: mgorman@suse.de > Cc: Andrew Morton > Signed-off-by: Joel Fernandes (Google) > --- > > This patch is based on the (not yet upstream) code in: > git://git.kernel.org/pub/scm/linux/kernel/git/jfern/linux.git (branch rcu/kfree) > > It is a follow-up to the posted series: > https://lore.kernel.org/lkml/20200330023248.164994-1-joel@joelfernandes.org/ > > > kernel/rcu/tree.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 4be763355c9fb..965deefffdd58 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -3149,7 +3149,7 @@ static inline struct rcu_head *attach_rcu_head_to_object(void *obj) > > if (!ptr) > ptr = kmalloc(sizeof(unsigned long *) + > - sizeof(struct rcu_head), GFP_ATOMIC | __GFP_NOWARN); > + sizeof(struct rcu_head), GFP_MEMALLOC); Just to add, the main requirements here are: 1. Allocation should be bounded in time. 2. Allocation should try hard (possibly tapping into reserves) 3. Sleeping is Ok but should not affect the time bound. Considering this, GFP_MEMALLOC|GFP_NOWAIT seems appropriate. Thoughts? thanks, - Joel