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=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 5D65CC433B4 for ; Wed, 7 Apr 2021 20:14:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 16C30611C1 for ; Wed, 7 Apr 2021 20:14:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355990AbhDGUPE (ORCPT ); Wed, 7 Apr 2021 16:15:04 -0400 Received: from server.lespinasse.org ([63.205.204.226]:37655 "EHLO server.lespinasse.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345885AbhDGUPE (ORCPT ); Wed, 7 Apr 2021 16:15:04 -0400 DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=lespinasse.org; i=@lespinasse.org; q=dns/txt; s=srv-11-ed; t=1617826493; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to : from; bh=1amBocSDkmECZ2mX+Wc/8c6p3WkPnn/9Znd0jYHQysk=; b=1utFFPbwYH/kug0197KEJXeIgLIxpJOV5kRZk+THEpmPkR5sjuxevNPszZCRqfhs8ZgzX VbSfwENbkDiOdRyAQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=lespinasse.org; i=@lespinasse.org; q=dns/txt; s=srv-11-rsa; t=1617826493; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to : from; bh=1amBocSDkmECZ2mX+Wc/8c6p3WkPnn/9Znd0jYHQysk=; b=DEKz1SQnJU+nbSR645NCzeOO9THxWML8a9p6boPQGis3vFpMhPs8PQr3QbgvxAvvHslCn TnhKABdkSqoraINfdiXolIpbGsG0/HyHkthR8o2pYO/JWkunCg/m+y7RM8Zy7J6URdLpNVk SrbcSf7rpUqx7pTecUuEMzu0BVnmRyLXVoag4y3hJaYEnTgKyhq4TUp5vp8CZfhv7OKuQEv nojZ9+GLYUKT9Jo6X5fdvc4cKeHtGjf44xHYzXfE2zJzFiAzThgkuA2Un8/FxNJnZA3uyGK j35FL2gSm+wkUNjp7p6Z21ee5TkA7Co3CZTRDEaUUtXUEZgLRMfz1QljNXhQ== Received: by server.lespinasse.org (Postfix, from userid 1000) id B8916160244; Wed, 7 Apr 2021 13:14:53 -0700 (PDT) Date: Wed, 7 Apr 2021 13:14:53 -0700 From: Michel Lespinasse To: Peter Zijlstra Cc: Michel Lespinasse , Linux-MM , Laurent Dufour , Michal Hocko , Matthew Wilcox , Rik van Riel , Paul McKenney , Andrew Morton , Suren Baghdasaryan , Joel Fernandes , Rom Lemarchand , Linux-Kernel Subject: Re: [RFC PATCH 11/37] x86/mm: attempt speculative mm faults first Message-ID: <20210407201453.GA25738@lespinasse.org> References: <20210407014502.24091-1-michel@lespinasse.org> <20210407014502.24091-12-michel@lespinasse.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 07, 2021 at 04:48:44PM +0200, Peter Zijlstra wrote: > On Tue, Apr 06, 2021 at 06:44:36PM -0700, Michel Lespinasse wrote: > > --- a/arch/x86/mm/fault.c > > +++ b/arch/x86/mm/fault.c > > @@ -1219,6 +1219,8 @@ void do_user_addr_fault(struct pt_regs *regs, > > struct mm_struct *mm; > > vm_fault_t fault; > > unsigned int flags = FAULT_FLAG_DEFAULT; > > + struct vm_area_struct pvma; > > That's 200 bytes on-stack... I suppose that's just about acceptible, but > perhaps we need a comment in struct vm_area_struct to make people aware > this things lives on-stack and size really is an issue now. Right, I agree that having the vma copy on-stack is not ideal. I think what really should be done, is to copy just the attributes of the vma that will be needed during the page fault. Things like vm_mm, vm_page_prot, vm_flags, vm_ops, vm_pgoff, vm_file, vm_private_data, vm_policy. We definitely do not need rbtree and rmap fields such as vm_prev, vm_next, vm_rb, rb_subtree_gap, shared, anon_vma_chain etc... The reason I did things this way, is because changing the entire fault handler to use attributes stored in struct vm_fault, rather than in the original vma, would be quite intrusive. I think it would be a reasonable step to consider once there is agreement on the rest of the speculative fault patch set, but it's practical doing it before then.