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=-8.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 28C4CC433E2 for ; Wed, 9 Sep 2020 16:02:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BE783206D4 for ; Wed, 9 Sep 2020 16:02:40 +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="GCZKbgAu" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730794AbgIIQCi (ORCPT ); Wed, 9 Sep 2020 12:02:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51572 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730572AbgIIP5f (ORCPT ); Wed, 9 Sep 2020 11:57:35 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BD524C0617BC; Wed, 9 Sep 2020 06:41:42 -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=BsLnzg0TUWFKkjHB7GFuV9Yd79wQB1MTmZ0FtnYyRyI=; b=GCZKbgAuJ6yV+SQqDvHW+6PyrE ab0uViZ1p2LiP11FDscTtRCp12Q3B340D3uZiwWo/XI8BPPVt287/xUcccpauyP/TaEjVOSS17/fm V9NJyyTEUONuX65JlwAquxfYIYkCKvFz07SWkSVVqFpQh7feNniyj9G/5CsLr2/Sd9YSVIzq4+UnS tVTXUmA6xKojbQLj0CgIhpctFkrSHO0Rc8qmGOUrtqSAQeb06fyDVo7psPozObT2tg0FtAbiwxUWO VM2JK2pz+Zknt3xxLEESLaklHGIjuQQPpqI2FCXR81KI7VExiSojqMf2AJvgJNoN5l8yfOrNm4WX5 eK16QwdQ==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kG0Lw-0003p4-CD; Wed, 09 Sep 2020 13:41:36 +0000 Date: Wed, 9 Sep 2020 14:41:36 +0100 From: Matthew Wilcox To: Christoph Hellwig Cc: Ming Mao , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, alex.williamson@redhat.com, akpm@linux-foundation.org, cohuck@redhat.com, jianjay.zhou@huawei.com, weidong.huang@huawei.com, peterx@redhat.com, aarcange@redhat.com, wangyunjian@huawei.com, jhubbard@nvidia.com Subject: Re: [PATCH V4 1/2] vfio dma_map/unmap: optimized for hugetlbfs pages Message-ID: <20200909134136.GG6583@casper.infradead.org> References: <20200908133204.1338-1-maoming.maoming@huawei.com> <20200908133204.1338-2-maoming.maoming@huawei.com> <20200909080114.GA8321@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200909080114.GA8321@infradead.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 09, 2020 at 09:01:14AM +0100, Christoph Hellwig wrote: > I really don't think this approach is any good. You workaround > a deficiency in the pin_user_pages API in one particular caller for > one particular use case. > > I think you'd rather want either: > > (1) a FOLL_HUGEPAGE flag for the pin_user_pages API family that returns > a single struct page for any kind of huge page, which would also > benefit all kinds of other users rather than adding these kinds of > hacks to vfio. This seems to be similar to a flag I added last week to pagecache_get_page() called FGP_HEAD: + * * %FGP_HEAD - If the page is present and a THP, return the head page + * rather than the exact page specified by the index. I think "return the head page" is probably what we want from what I understand of this patch. The caller can figure out the appropriate bv_offset / bv_len for a bio_vec, if that's what they want to do with it. http://git.infradead.org/users/willy/pagecache.git/commitdiff/ee88eeeb6b0f35e95ef82b11dfc24dc04c3dcad8 is the exact commit where I added that, but it depends on a number of other patches in this series: http://git.infradead.org/users/willy/pagecache.git/shortlog I'm going to send out a subset of patches later today which will include that one and some others. I haven't touched the GUP paths at all in that series, but it's certainly going to make THPs (of various sizes) much more present in the system.