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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 1DFCDC432C1 for ; Tue, 24 Sep 2019 15:45:28 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C7A2F21783 for ; Tue, 24 Sep 2019 15:45:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="jTeTNKav" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C7A2F21783 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 6974B6B0007; Tue, 24 Sep 2019 11:45:27 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 648D46B000C; Tue, 24 Sep 2019 11:45:27 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 537086B000E; Tue, 24 Sep 2019 11:45:27 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0037.hostedemail.com [216.40.44.37]) by kanga.kvack.org (Postfix) with ESMTP id 311D16B0007 for ; Tue, 24 Sep 2019 11:45:27 -0400 (EDT) Received: from smtpin03.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id 6EDAA8243781 for ; Tue, 24 Sep 2019 15:45:26 +0000 (UTC) X-FDA: 75970238652.03.tooth83_86b1193eec147 X-HE-Tag: tooth83_86b1193eec147 X-Filterd-Recvd-Size: 7055 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Tue, 24 Sep 2019 15:45:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=jOfR9f04JOdM45K4qEfyjOiS102zGBwkqhbp9cILr54=; b=jTeTNKavnzWQmuz8rP0rGwEdF +y4XPaqQc9k8kMo4jiHGsbF63UCJsAKGtjbqcRCYyHuJ2wi8bHMsCKFMhsev2a3tibjtKH2g7GGuP GyBrxiaVFTLjMIV3R82zC1YOkkqcgFWPmbcy/FKqmLNsWzeWIqtQG9tmHssSN/lZdT2ciOsDJs3TV cSUSUWfUXeU6sfMEIjVdEOzib431n5HZeR/JUaxp2tT2p5XwJU0mfDp6INWj+TAeg8/ByM/SnIllx tdWoYf0qvTys70NsMosJkvgGIDdjiHIpVrCcD0N+PmbegflbquPV6qmihfj/1E9zbSPJZMlk73xoQ LFhP/JxwA==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.2 #3 (Red Hat Linux)) id 1iCn0A-0007Gx-R2; Tue, 24 Sep 2019 15:45:18 +0000 Date: Tue, 24 Sep 2019 08:45:18 -0700 From: Matthew Wilcox To: Peter Xu Cc: Linus Torvalds , Linux-MM , Linux Kernel Mailing List , David Hildenbrand , Hugh Dickins , Maya Gokhale , Jerome Glisse , Pavel Emelyanov , Johannes Weiner , Martin Cracauer , Marty McFadden , Shaohua Li , Andrea Arcangeli , Mike Kravetz , Denis Plotnikov , Mike Rapoport , Mel Gorman , "Kirill A . Shutemov" , "Dr . David Alan Gilbert" Subject: Re: [PATCH v4 05/10] mm: Return faster for non-fatal signals in user mode faults Message-ID: <20190924154518.GG1855@bombadil.infradead.org> References: <20190923042523.10027-1-peterx@redhat.com> <20190923042523.10027-6-peterx@redhat.com> <20190924024721.GD28074@xz-x1> <20190924025447.GE1855@bombadil.infradead.org> <20190924031908.GF28074@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190924031908.GF28074@xz-x1> User-Agent: Mutt/1.12.1 (2019-06-15) 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 Tue, Sep 24, 2019 at 11:19:08AM +0800, Peter Xu wrote: > On Mon, Sep 23, 2019 at 07:54:47PM -0700, Matthew Wilcox wrote: > > On Tue, Sep 24, 2019 at 10:47:21AM +0800, Peter Xu wrote: > > > On Mon, Sep 23, 2019 at 11:03:49AM -0700, Linus Torvalds wrote: > > > > On Sun, Sep 22, 2019 at 9:26 PM Peter Xu wrote: > > > > > > > > > > This patch is a preparation of removing that special path by allowing > > > > > the page fault to return even faster if we were interrupted by a > > > > > non-fatal signal during a user-mode page fault handling routine. > > > > > > > > So I really wish saome other vm person would also review these things, > > > > but looking over this series once more, this is the patch I probably > > > > like the least. > > > > > > > > And the reason I like it the least is that I have a hard time > > > > explaining to myself what the code does and why, and why it's so full > > > > of this pattern: > > > > > > > > > - if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) > > > > > + if ((fault & VM_FAULT_RETRY) && > > > > > + fault_should_check_signal(user_mode(regs))) > > > > > return; > > > > > > > > which isn't all that pretty. > > > > > > > > Why isn't this just > > > > > > > > static bool fault_signal_pending(unsigned int fault_flags, struct > > > > pt_regs *regs) > > > > { > > > > return (fault_flags & VM_FAULT_RETRY) && > > > > (fatal_signal_pending(current) || > > > > (user_mode(regs) && signal_pending(current))); > > > > } > > > > > > > > and then most of the users would be something like > > > > > > > > if (fault_signal_pending(fault, regs)) > > > > return; > > > > > > > > and the exceptions could do their own thing. > > > > > > > > Now the code is prettier and more understandable, I feel. > > > > > > > > And if something doesn't follow this pattern, maybe it either _should_ > > > > follow that pattern or it should just not use the helper but explain > > > > why it has an unusual pattern. > > > > > +++ b/arch/alpha/mm/fault.c > > > @@ -150,7 +150,7 @@ do_page_fault(unsigned long address, unsigned long mmcsr, > > > the fault. */ > > > fault = handle_mm_fault(vma, address, flags); > > > > > > - if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) > > > + if (fault_signal_pending(fault, regs)) > > > return; > > > > > > if (unlikely(fault & VM_FAULT_ERROR)) { > > > > > +++ b/arch/arm/mm/fault.c > > > @@ -301,6 +301,11 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs) > > > return 0; > > > } > > > > > > + /* Fast path to handle user mode signals */ > > > + if ((fault & VM_FAULT_RETRY) && user_mode(regs) && > > > + signal_pending(current)) > > > + return 0; > > > > But _why_ are they different? This is a good opportunity to make more > > code the same between architectures. > > (Thanks for joining the discussion) > > I'd like to do these - my only worry is that I can't really test them > well simply because I don't have all the hardwares. For now the > changes are mostly straightforward so I'm relatively confident (not to > mention the code needs proper reviews too, and of course I would > appreciate much if anyone wants to smoke test it). If I change it in > a drastic way, I won't be that confident without some tests at least > on multiple archs (not to mention that even smoke testing across major > archs will be a huge amount of work...). So IMHO those might be more > suitable as follow-up for per-arch developers if we can at least reach > a consensus on the whole idea of this patchset. I think the way to do this is to introduce fault_signal_pending(), converting the architectures to it that match that pattern. Then one patch per architecture to convert the ones which use a different pattern to the same pattern. Oh, and while you're looking at the callers of handle_mm_fault(), a lot of them don't check conditions in the right order. x86, at least, handles FAULT_RETRY before handling FAULT_ERROR, which is clearly wrong. Kirill and I recently discussed it here: https://lore.kernel.org/linux-mm/20190911152338.gqqgxrmqycodfocb@box/T/