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=-0.6 required=3.0 tests=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 A13A3C33CB1 for ; Wed, 15 Jan 2020 15:30:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 76A6B222C3 for ; Wed, 15 Jan 2020 15:30:42 +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="KTafuKCn" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726506AbgAOPal (ORCPT ); Wed, 15 Jan 2020 10:30:41 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:50916 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726132AbgAOPal (ORCPT ); Wed, 15 Jan 2020 10:30:41 -0500 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=hlxbWHBq8lfTBkbbWblALE5WfMIrcmCMtir+afT5h7g=; b=KTafuKCnLEQxrDndx0KF1DZxC rnKdoLI6sypMh61W+oBSzZckG9nErVqXpqRux90/jnJHBoNxCmDRhLN16rsx5kcLMMQTzpNlRHW3V Kn+EfBOj9xXDn+MMy1P1Ce1dDs4zbgiDeuR8jQgZiUt61hA4+gx5SghScUnsRQG1ziTZYHV9R9Zgf pJxhgaR5AeWS3+N32IQliDA3Jqotb5XQKegSIoZaLpNN+GhynXNs1L5cGpIhmQbJynCGULBXCRnjC vAgzg7hshbf2g9UxNsiPKchC1nKbZKVYFzdAbYAS/fNwV5Y2i+QhIqJe1mPDizEBhtnZaTAQECgQV KQqONFysg==; Received: from hch by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1irkce-0002dy-Qu; Wed, 15 Jan 2020 15:30:20 +0000 Date: Wed, 15 Jan 2020 07:30:20 -0800 From: Christoph Hellwig To: John Hubbard Cc: Andrew Morton , Al Viro , Alex Williamson , Benjamin Herrenschmidt , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Christoph Hellwig , Dan Williams , Daniel Vetter , Dave Chinner , David Airlie , "David S . Miller" , Ira Weiny , Jan Kara , Jason Gunthorpe , Jens Axboe , Jonathan Corbet , =?iso-8859-1?B?Suly9G1l?= Glisse , "Kirill A . Shutemov" , Magnus Karlsson , Mauro Carvalho Chehab , Michael Ellerman , Michal Hocko , Mike Kravetz , Paul Mackerras , Shuah Khan , Vlastimil Babka , bpf@vger.kernel.org, dri-devel@lists.freedesktop.org, kvm@vger.kernel.org, linux-block@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org, linux-rdma@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-mm@kvack.org, LKML , Mike Rapoport Subject: Re: [PATCH v12 11/22] mm/gup: introduce pin_user_pages*() and FOLL_PIN Message-ID: <20200115153020.GF19546@infradead.org> References: <20200107224558.2362728-1-jhubbard@nvidia.com> <20200107224558.2362728-12-jhubbard@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200107224558.2362728-12-jhubbard@nvidia.com> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Tue, Jan 07, 2020 at 02:45:47PM -0800, John Hubbard wrote: > Introduce pin_user_pages*() variations of get_user_pages*() calls, > and also pin_longterm_pages*() variations. > > For now, these are placeholder calls, until the various call sites > are converted to use the correct get_user_pages*() or > pin_user_pages*() API. What do the pure placeholders buy us? The API itself looks ok, but until it actually is properly implemented it doesn't help at all, and we've had all kinds of bad experiences with these sorts of stub APIs.