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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 7B7ECC433ED for ; Wed, 7 Apr 2021 02:36:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3D4926124B for ; Wed, 7 Apr 2021 02:36:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348110AbhDGCgn (ORCPT ); Tue, 6 Apr 2021 22:36:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60866 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233994AbhDGCgj (ORCPT ); Tue, 6 Apr 2021 22:36:39 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 431E2C06174A for ; Tue, 6 Apr 2021 19:36:30 -0700 (PDT) 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=v2HTiDurUhaFtku9x3Aod8jwLxk/iaIfkceEVuQR2iU=; b=u3XibzCpDyGFKLZZNeLqPUf+Yj K2MaxDOG6QRHihh3SvSIpyISf/sC7iSz/PFCCgXiggJUG+/8yYEC1IU9v7T40IHII6ul12Yo7Lauh LlmUiLOhspkllYcGx1KeBHdUyPdx06f3HCXeGKih+W43Az8YyReJyjl7ekMOuy5nPeYev0/Y/WN6c oOgil/cRFKflduositqm7FIOZeZwFIN2yg6q19hKQ92Wxs+MGdS1UqgRQ5vO/xbh/TBXhpaha943d X7hZfkCg+DT1TtxvsnFj+lmzoQjh6FSYDqumoFCluvyDFInZqxFst1yykAxT7WKK6D94Uo0mOi6tr R65Cs/TA==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1lTy2R-00Dm0l-9W; Wed, 07 Apr 2021 02:35:31 +0000 Date: Wed, 7 Apr 2021 03:35:27 +0100 From: Matthew Wilcox To: Michel Lespinasse Cc: Linux-MM , Laurent Dufour , Peter Zijlstra , Michal Hocko , Rik van Riel , Paul McKenney , Andrew Morton , Suren Baghdasaryan , Joel Fernandes , Rom Lemarchand , Linux-Kernel Subject: Re: [RFC PATCH 24/37] mm: implement speculative handling in __do_fault() Message-ID: <20210407023527.GX2531743@casper.infradead.org> References: <20210407014502.24091-1-michel@lespinasse.org> <20210407014502.24091-25-michel@lespinasse.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210407014502.24091-25-michel@lespinasse.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 06, 2021 at 06:44:49PM -0700, Michel Lespinasse wrote: > In the speculative case, call the vm_ops->fault() method from within > an rcu read locked section, and verify the mmap sequence lock at the > start of the section. A match guarantees that the original vma is still > valid at that time, and that the associated vma->vm_file stays valid > while the vm_ops->fault() method is running. > > Note that this implies that speculative faults can not sleep within > the vm_ops->fault method. We will only attempt to fetch existing pages > from the page cache during speculative faults; any miss (or prefetch) > will be handled by falling back to non-speculative fault handling. > > The speculative handling case also does not preallocate page tables, > as it is always called with a pre-existing page table. I still don't understand why you want to do this. The speculative fault that doesn't do I/O is already here, and it's called ->map_pages (which I see you also do later). So what's the point of this patch?