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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6483DC6FA82 for ; Mon, 5 Sep 2022 02:32:26 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BE00D8D004F; Sun, 4 Sep 2022 22:32:25 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B8E8E8D0030; Sun, 4 Sep 2022 22:32:25 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A56058D004F; Sun, 4 Sep 2022 22:32:25 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 96ACA8D0030 for ; Sun, 4 Sep 2022 22:32:25 -0400 (EDT) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 576E9804E7 for ; Mon, 5 Sep 2022 02:32:25 +0000 (UTC) X-FDA: 79876457850.11.F8BA2FE Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by imf30.hostedemail.com (Postfix) with ESMTP id 133CD80083 for ; Mon, 5 Sep 2022 02:32:23 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4MLXVb1F5wzWfLT; Mon, 5 Sep 2022 10:27:51 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Mon, 5 Sep 2022 10:32:18 +0800 Subject: Re: [PATCH 7/8] hugetlb: create hugetlb_unmap_file_folio to unmap single file folio To: Mike Kravetz CC: Muchun Song , David Hildenbrand , Michal Hocko , Peter Xu , Naoya Horiguchi , "Aneesh Kumar K . V" , Andrea Arcangeli , "Kirill A . Shutemov" , Davidlohr Bueso , Prakash Sangappa , James Houghton , Mina Almasry , Pasha Tatashin , Axel Rasmussen , Ray Fucillo , Andrew Morton , , References: <20220824175757.20590-1-mike.kravetz@oracle.com> <20220824175757.20590-8-mike.kravetz@oracle.com> <0e31f9da-5953-2f44-1a59-888e3313e919@huawei.com> <304a6d9a-9029-8ee8-7205-d0ef4a5403bd@huawei.com> From: Miaohe Lin Message-ID: <5dc9b069-7268-3123-2891-881977cb42dd@huawei.com> Date: Mon, 5 Sep 2022 10:32:17 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662345145; a=rsa-sha256; cv=none; b=nQ/GVzZlCoy+35aZaF8MAix2SicJZ9XYnFmdcNAmESlFN6sXLYbaAHf+vGmV+nH+2w5LCh KD0WwKP9ruDt07j8aNWhTd/zEFhAZqo4GRq8aPoJWJYJOg2+rbR5mEFKCiWnKAm960+680 5244wWWmTkvFTmKA/iHB3Frpd1mKDlE= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=none; spf=pass (imf30.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1662345145; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=JShOeNEPr6qR8aSUwxj/79ZchHGtLxjGXCDtnYSelCQ=; b=JJi+YlajY+KlSq8iqumEnpaj6NluaVHVpoUeEUpGcWKHa06ImyQEnt2Arm6lAIMgKwxj4T XLr+8QOjmKTQO0m0LQPNS4Cz/LPIjHLSF+nM5fcGxLpdG/nSsoFNzn6JtyB+2QzUz5ONOh BNgyb0RK8b5xjQvOJpnvUAkvGlEYAKM= X-Rspam-User: X-Stat-Signature: 433w8yis7naj5u5b8nufw4htpppgu6ir X-Rspamd-Queue-Id: 133CD80083 X-Rspamd-Server: rspam10 Authentication-Results: imf30.hostedemail.com; dkim=none; spf=pass (imf30.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-HE-Tag: 1662345143-210859 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 2022/9/3 5:35, Mike Kravetz wrote: > On 08/30/22 10:46, Miaohe Lin wrote: >> On 2022/8/30 6:37, Mike Kravetz wrote: >>> On 08/29/22 10:44, Miaohe Lin wrote: >>>> On 2022/8/25 1:57, Mike Kravetz wrote: >>>>> Create the new routine hugetlb_unmap_file_folio that will unmap a single >>>>> file folio. This is refactored code from hugetlb_vmdelete_list. It is >>>>> modified to do locking within the routine itself and check whether the >>>>> page is mapped within a specific vma before unmapping. >>>>> >>>>> This refactoring will be put to use and expanded upon in a subsequent >>>>> patch adding vma specific locking. >>>>> >>>>> Signed-off-by: Mike Kravetz >>>>> --- >>>>> fs/hugetlbfs/inode.c | 123 +++++++++++++++++++++++++++++++++---------- >>>>> 1 file changed, 94 insertions(+), 29 deletions(-) >>>>> >>>>> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c >>>>> index e83fd31671b3..b93d131b0cb5 100644 >>>>> --- a/fs/hugetlbfs/inode.c >>>>> +++ b/fs/hugetlbfs/inode.c >>>>> @@ -371,6 +371,94 @@ static void hugetlb_delete_from_page_cache(struct page *page) >>>>> delete_from_page_cache(page); >>>>> } >>>>> >>>>> +/* >>>>> + * Called with i_mmap_rwsem held for inode based vma maps. This makes >>>>> + * sure vma (and vm_mm) will not go away. We also hold the hugetlb fault >>>>> + * mutex for the page in the mapping. So, we can not race with page being >>>>> + * faulted into the vma. >>>>> + */ >>>>> +static bool hugetlb_vma_maps_page(struct vm_area_struct *vma, >>>>> + unsigned long addr, struct page *page) >>>>> +{ >>>>> + pte_t *ptep, pte; >>>>> + >>>>> + ptep = huge_pte_offset(vma->vm_mm, addr, >>>>> + huge_page_size(hstate_vma(vma))); >>>>> + >>>>> + if (!ptep) >>>>> + return false; >>>>> + >>>>> + pte = huge_ptep_get(ptep); >>>>> + if (huge_pte_none(pte) || !pte_present(pte)) >>>>> + return false; >>>>> + >>>>> + if (pte_page(pte) == page) >>>>> + return true; >>>> >>>> I'm thinking whether pte entry could change after we check it since huge_pte_lock is not held here. >>>> But I think holding i_mmap_rwsem in writelock mode should give us such a guarantee, e.g. migration >>>> entry is changed back to huge pte entry while holding i_mmap_rwsem in readlock mode. >>>> Or am I miss something? >>> >>> Let me think about this. I do not think it is possible, but you ask good >>> questions. >>> >>> Do note that this is the same locking sequence used at the beginning of the >>> page fault code where the decision to call hugetlb_no_page() is made. >> >> Yes, hugetlb_fault() can tolerate the stale pte entry because pte entry will be re-checked later under the page table lock. >> However if we see a stale pte entry here, the page might be leftover after truncated and thus break truncation? But I'm not >> sure whether this will occur. Maybe the i_mmap_rwsem writelock and hugetlb_fault_mutex can prevent this issue. >> > > I looked at this some more. Just to be clear, we only need to worry > about modifications of pte_page(). Racing with other pte modifications > such as accessed, or protection changes is acceptable. > > Of course, the fault mutex prevents faults from happening. i_mmap_rwsem > protects against unmap and truncation operations as well as migration as > you noted above. I believe the only other place where we update pte_page() > is when copying page table such as during fork. However, with commit > bcd51a3c679d "Lazy page table copies in fork()" we are going to skip > copying for files and rely on page faults to populate the tables. > > I believe we are safe from races with just the fault mutex and i_mmap_rwsem. I believe your analysis is right. Thanks for your clarifying. Thanks, Miaohe Lin