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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 A7105C433DB for ; Fri, 26 Feb 2021 16:04:14 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 04CAD64E28 for ; Fri, 26 Feb 2021 16:04:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 04CAD64E28 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 8CB358D0001; Fri, 26 Feb 2021 11:04:13 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 87A506B0070; Fri, 26 Feb 2021 11:04:13 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 76A708D0001; Fri, 26 Feb 2021 11:04:13 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0052.hostedemail.com [216.40.44.52]) by kanga.kvack.org (Postfix) with ESMTP id 5EDDA6B006E for ; Fri, 26 Feb 2021 11:04:13 -0500 (EST) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 28686824805A for ; Fri, 26 Feb 2021 16:04:13 +0000 (UTC) X-FDA: 77860890786.02.A0E3BA4 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf11.hostedemail.com (Postfix) with ESMTP id A6D9720053D8 for ; Fri, 26 Feb 2021 16:03:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=nlrPN6RKsKi94KSjI+2dR6vaJd54WtU/wGcRKq1SGac=; b=ONNF7yjdRI1tRIpo0PQk8cAljg u3YfDpfRVp8NNTh+ucghqkv8ngoXtpV/axBTq+P3Js4/AgyZgZ+aekEOAxYXOgmJ79Hs1Dv9GhdgP lX3X4f0Fk5rpkhvUZD135Bxge8SpbXgAWybC2Mc3IKg3MN09I5BSb50Xa+8zU8k06Bq9FTNaxAdo+ 3yACY5ecnhSeenvfblbCjWFkZUpNoCN1FOipQcGGa0h3ERmwuB8zyX+2Ub/weelZ0uph9wN5CPbRO SBH78t+9xvcw1R03B/mfNcNRPENtIas77/vSrsXz649FAQPO+oDNpa6wrW/A0DObSZ2Hw+inIYCx9 /OSQsC6g==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lFfas-00CDLc-Ux; Fri, 26 Feb 2021 16:03:59 +0000 Date: Fri, 26 Feb 2021 16:03:54 +0000 From: Matthew Wilcox To: Jason Gunthorpe Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: Freeing page tables through RCU Message-ID: <20210226160354.GE2723601@casper.infradead.org> References: <20210225205820.GC2858050@casper.infradead.org> <20210226144200.GV2643399@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210226144200.GV2643399@ziepe.ca> X-Stat-Signature: qc8qsaqptazc6zk3yzcbsqmrq9qimudk X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: A6D9720053D8 Received-SPF: none (infradead.org>: No applicable sender policy available) receiver=imf11; identity=mailfrom; envelope-from=""; helo=casper.infradead.org; client-ip=90.155.50.34 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1614355439-199129 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Feb 26, 2021 at 10:42:00AM -0400, Jason Gunthorpe wrote: > On Thu, Feb 25, 2021 at 08:58:20PM +0000, Matthew Wilcox wrote: > > > I'd like to hear better ideas than this. > > You didn't like my suggestion to put a sleepable lock around the > freeing of page tables during flushing? > > I still don't see how you convert the sleepable page walkers to use > rcu?? I don't want to convert the sleepable ones to use RCU ... I want to convert the non-sleeping ones to use RCU. A page_table_free_lock might work, but it might have its own problems later (eg a sleeping lock can't be acquired under RCU or spinlock, and it can't be a spinlock because it'd have to be held while we wait for IPIs). I think it would solve my immediate problem, and I wonder if it might solve some other problems ...