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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 36F71C35247 for ; Mon, 3 Feb 2020 21:01:18 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id DAE0F2087E for ; Mon, 3 Feb 2020 21:01:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="ZlOdaNKe" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DAE0F2087E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=nvidia.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 82E896B0003; Mon, 3 Feb 2020 16:01:17 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7DEB76B0005; Mon, 3 Feb 2020 16:01:17 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6F47B6B0006; Mon, 3 Feb 2020 16:01:17 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0235.hostedemail.com [216.40.44.235]) by kanga.kvack.org (Postfix) with ESMTP id 589BE6B0003 for ; Mon, 3 Feb 2020 16:01:17 -0500 (EST) Received: from smtpin05.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 1876C180AD804 for ; Mon, 3 Feb 2020 21:01:17 +0000 (UTC) X-FDA: 76450036194.05.toe62_6267d3a09703e X-HE-Tag: toe62_6267d3a09703e X-Filterd-Recvd-Size: 6243 Received: from hqnvemgate25.nvidia.com (hqnvemgate25.nvidia.com [216.228.121.64]) by imf21.hostedemail.com (Postfix) with ESMTP for ; Mon, 3 Feb 2020 21:01:16 +0000 (UTC) Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate25.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Mon, 03 Feb 2020 13:00:51 -0800 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Mon, 03 Feb 2020 13:01:14 -0800 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Mon, 03 Feb 2020 13:01:14 -0800 Received: from [10.110.48.28] (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Mon, 3 Feb 2020 21:01:14 +0000 Subject: Re: [PATCH v3 07/12] mm/gup: track FOLL_PIN pages To: "Kirill A. Shutemov" CC: Andrew Morton , Al Viro , Christoph Hellwig , Dan Williams , Dave Chinner , Ira Weiny , Jan Kara , Jason Gunthorpe , Jonathan Corbet , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Michal Hocko , Mike Kravetz , Shuah Khan , Vlastimil Babka , Matthew Wilcox , , , , , , LKML , "Kirill A . Shutemov" References: <20200201034029.4063170-1-jhubbard@nvidia.com> <20200201034029.4063170-8-jhubbard@nvidia.com> <20200203134024.htczuqghduajb3yx@box> X-Nvconfidentiality: public From: John Hubbard Message-ID: <44f9e71f-dc65-fb37-dd6d-228270170aad@nvidia.com> Date: Mon, 3 Feb 2020 13:01:14 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.2 MIME-Version: 1.0 In-Reply-To: <20200203134024.htczuqghduajb3yx@box> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL111.nvidia.com (172.20.187.18) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1580763651; bh=xdyrRhrFRwm8PgNsPaTnG7fESTt9E/IE4SCifoyTh/g=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=ZlOdaNKeCwGQCefKwQkyzz5HO3exK9puspru1qNqq8OeTYhh79QWmjMtrfnso5+/i okdRSSlKjbVj6W3rH8UK/+NXzDNQQSIFzmO/yAxm2o28hb6D9mOZq7R3erjxiHtkJg Pq9boyDlD9aiomyCHOcEdWTjh1LL6mxNXdSseAKDijaCu8YQP9ylcUSgfrO+BG3Ktk 5dNjBCi3KJfawkDCi9Laqgj825rrHLwsKcNDBOAjF5PR8AbP2BDizrMjAO0QnCE6LA BNJqk2jhW8zGG9ac3sM5E6VfkmA1W1V1JqBYxqnsaL6hHsS+lzpNh3QdGs6DPM5mbC 6hWoULMfVb8tg== 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 2/3/20 5:40 AM, Kirill A. Shutemov wrote: > On Fri, Jan 31, 2020 at 07:40:24PM -0800, John Hubbard wrote: >> @@ -4405,7 +4392,13 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, >> same_page: >> if (pages) { >> pages[i] = mem_map_offset(page, pfn_offset); >> - get_page(pages[i]); >> + if (!try_grab_page(pages[i], flags)) { >> + spin_unlock(ptl); >> + remainder = 0; >> + err = -ENOMEM; >> + WARN_ON_ONCE(1); > > The WARN_ON_ONCE deserve a comment. And I guess you can put it into 'if' > condition. OK, I've changed it to the following, which I *think* is an accurate comment, but I'm still a bit new to huge pages: if (pages) { pages[i] = mem_map_offset(page, pfn_offset); /* * try_grab_page() should always succeed here, because: * a) we hold the ptl lock, and b) we've just checked * that the huge page is present in the page tables. If * the huge page is present, then the tail pages must * also be present. The ptl prevents the head page and * tail pages from being rearranged in any way. So this * page must be available at this point, unless the page * refcount overflowed: */ if (WARN_ON_ONCE(!try_grab_page(pages[i], flags))) { spin_unlock(ptl); remainder = 0; err = -ENOMEM; break; } } > >> + break; >> + } >> } >> >> if (vmas) >> @@ -4965,6 +4958,12 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, >> struct page *page = NULL; >> spinlock_t *ptl; >> pte_t pte; >> + >> + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ >> + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == >> + (FOLL_PIN | FOLL_GET))) >> + return NULL; >> + >> retry: >> ptl = pmd_lockptr(mm, pmd); >> spin_lock(ptl); >> @@ -4977,8 +4976,11 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address, >> pte = huge_ptep_get((pte_t *)pmd); >> if (pte_present(pte)) { >> page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT); >> - if (flags & FOLL_GET) >> - get_page(page); >> + if (unlikely(!try_grab_page(page, flags))) { >> + WARN_ON_ONCE(1); > > Ditto. OK, I've added a similar comment as the one above. Now it looks like this: if (pte_present(pte)) { page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT); /* * try_grab_page() should always succeed here, because: a) we * hold the pmd (ptl) lock, and b) we've just checked that the * huge pmd (head) page is present in the page tables. The ptl * prevents the head page and tail pages from being rearranged * in any way. So this page must be available at this point, * unless the page refcount overflowed: */ if (WARN_ON_ONCE(!try_grab_page(page, flags))) { page = NULL; goto out; } thanks, -- John Hubbard NVIDIA > >> + page = NULL; >> + goto out; >> + } >> } else { >> if (is_hugetlb_entry_migration(pte)) { >> spin_unlock(ptl); >