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 1B719C4332F for ; Fri, 7 Jan 2022 14:44:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347845AbiAGOo6 (ORCPT ); Fri, 7 Jan 2022 09:44:58 -0500 Received: from smtp-out1.suse.de ([195.135.220.28]:58138 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347793AbiAGOo4 (ORCPT ); Fri, 7 Jan 2022 09:44:56 -0500 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id EFB46212C7; Fri, 7 Jan 2022 14:44:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1641566694; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=h+izeRbXwrcTs43CEeqEXv+4wDW5wqLoC+ZvbrCEav4=; b=m3hga6iQl2WdcE2aPXfiLHIDIlm90X2+/UUEe5oBUxt1WKdURAf4jx8f7kkkPymSP1I+ad kF55jxo7kAuCghJXeVUMqfESh/pQi0j8mDLAFcbEqvmoARN0dSUHtvsk1sQTwYYomJICL5 S6BjW+1PsU9wseHfa5980DYfHTG8dr4= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 3EA46A3B88; Fri, 7 Jan 2022 14:44:54 +0000 (UTC) Date: Fri, 7 Jan 2022 15:44:50 +0100 From: Michal Hocko To: Yu Zhao Cc: Andrew Morton , Linus Torvalds , Andi Kleen , Catalin Marinas , Dave Hansen , Hillf Danton , Jens Axboe , Jesse Barnes , Johannes Weiner , Jonathan Corbet , Matthew Wilcox , Mel Gorman , Michael Larabel , Rik van Riel , Vlastimil Babka , Will Deacon , Ying Huang , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, page-reclaim@google.com, x86@kernel.org, Konstantin Kharlamov Subject: Re: [PATCH v6 6/9] mm: multigenerational lru: aging Message-ID: References: <20220104202227.2903605-1-yuzhao@google.com> <20220104202227.2903605-7-yuzhao@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220104202227.2903605-7-yuzhao@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 04-01-22 13:22:25, Yu Zhao wrote: [...] > +static void walk_mm(struct lruvec *lruvec, struct mm_struct *mm, struct lru_gen_mm_walk *walk) > +{ > + static const struct mm_walk_ops mm_walk_ops = { > + .test_walk = should_skip_vma, > + .p4d_entry = walk_pud_range, > + }; > + > + int err; > +#ifdef CONFIG_MEMCG > + struct mem_cgroup *memcg = lruvec_memcg(lruvec); > +#endif > + > + walk->next_addr = FIRST_USER_ADDRESS; > + > + do { > + unsigned long start = walk->next_addr; > + unsigned long end = mm->highest_vm_end; > + > + err = -EBUSY; > + > + rcu_read_lock(); > +#ifdef CONFIG_MEMCG > + if (memcg && atomic_read(&memcg->moving_account)) > + goto contended; > +#endif > + if (!mmap_read_trylock(mm)) > + goto contended; Have you evaluated the behavior under mmap_sem contention? I mean what would be an effect of some mms being excluded from the walk? This path is called from direct reclaim and we do allocate with exclusive mmap_sem IIRC and the trylock can fail in a presence of pending writer if I am not mistaken so even the read lock holder (e.g. an allocation from the #PF) can bypass the walk. Or is this considered statistically insignificant thus a theoretical problem? -- Michal Hocko SUSE Labs