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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C3936C352A1 for ; Tue, 6 Dec 2022 11:29:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234786AbiLFL3F (ORCPT ); Tue, 6 Dec 2022 06:29:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34376 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234563AbiLFL2v (ORCPT ); Tue, 6 Dec 2022 06:28:51 -0500 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C7C89E48 for ; Tue, 6 Dec 2022 03:28:48 -0800 (PST) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.55]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4NRJ7M2YcTz15Mxx; Tue, 6 Dec 2022 19:27:59 +0800 (CST) Received: from [10.174.151.185] (10.174.151.185) 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 15.1.2375.31; Tue, 6 Dec 2022 19:28:45 +0800 Subject: Re: [PATCH v4 12/17] mm: remember exclusively mapped anonymous pages with PG_anon_exclusive To: David Hildenbrand , CC: Andrew Morton , Hugh Dickins , Linus Torvalds , David Rientjes , Shakeel Butt , John Hubbard , Jason Gunthorpe , Mike Kravetz , Mike Rapoport , Yang Shi , "Kirill A . Shutemov" , Matthew Wilcox , Vlastimil Babka , Jann Horn , Michal Hocko , Nadav Amit , Rik van Riel , Roman Gushchin , Andrea Arcangeli , Peter Xu , Donald Dutile , Christoph Hellwig , Oleg Nesterov , Jan Kara , Liang Zhang , Pedro Gomes , Oded Gabbay , References: <20220428083441.37290-1-david@redhat.com> <20220428083441.37290-13-david@redhat.com> <90dd6a93-4500-e0de-2bf0-bf522c311b0c@huawei.com> <3c7fd5da-b3f8-5562-45a9-f83d7dbcdd7d@redhat.com> From: Miaohe Lin Message-ID: <954b0bd3-bf7d-5c4b-5d76-8ac13b5ee8ac@huawei.com> Date: Tue, 6 Dec 2022 19:28:45 +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: 8bit X-Originating-IP: [10.174.151.185] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/12/6 17:40, David Hildenbrand wrote: > On 06.12.22 10:37, Miaohe Lin wrote: >> On 2022/12/6 16:43, David Hildenbrand wrote: >>>>> >>>> >>>> Hi David, sorry for the late respond and a possible inconsequential question. :) >>> >>> Better late than never! Thanks for the review, independently at which time it happens :) >>> >>>> >>>> >>>> >>>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>>>> index 7a71ed679853..5add8bbd47cd 100644 >>>>> --- a/mm/hugetlb.c >>>>> +++ b/mm/hugetlb.c >>>>> @@ -4772,7 +4772,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, >>>>>                        is_hugetlb_entry_hwpoisoned(entry))) { >>>>>                swp_entry_t swp_entry = pte_to_swp_entry(entry); >>>>>    -            if (is_writable_migration_entry(swp_entry) && cow) { >>>>> +            if (!is_readable_migration_entry(swp_entry) && cow) { >>>>>                    /* >>>>>                     * COW mappings require pages in both >>>>>                     * parent and child to be set to read. >>>>> @@ -5172,6 +5172,8 @@ static vm_fault_t hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma, >>>>>            set_huge_ptep_writable(vma, haddr, ptep); >>>>>            return 0; >>>>>        } >>>>> +    VM_BUG_ON_PAGE(PageAnon(old_page) && PageAnonExclusive(old_page), >>>>> +               old_page); >>>>>          /* >>>>>         * If the process that created a MAP_PRIVATE mapping is about to >>>>> @@ -6169,12 +6171,17 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, >>>>>            } >>>>>            if (unlikely(is_hugetlb_entry_migration(pte))) { >>>>>                swp_entry_t entry = pte_to_swp_entry(pte); >>>>> +            struct page *page = pfn_swap_entry_to_page(entry); >>>>>    -            if (is_writable_migration_entry(entry)) { >>>>> +            if (!is_readable_migration_entry(entry)) { >>>> >>>> In hugetlb_change_protection(), is_writable_migration_entry() is changed to !is_readable_migration_entry(), >>>> but >>>> >>>>>                    pte_t newpte; >>>>>    -                entry = make_readable_migration_entry( >>>>> -                            swp_offset(entry)); >>>>> +                if (PageAnon(page)) >>>>> +                    entry = make_readable_exclusive_migration_entry( >>>>> +                                swp_offset(entry)); >>>>> +                else >>>>> +                    entry = make_readable_migration_entry( >>>>> +                                swp_offset(entry)); >>>>>                    newpte = swp_entry_to_pte(entry); >>>>>                    set_huge_swap_pte_at(mm, address, ptep, >>>>>                                 newpte, huge_page_size(h)); >>>> >>>> >>>> >>>>> diff --git a/mm/mprotect.c b/mm/mprotect.c >>>>> index b69ce7a7b2b7..56060acdabd3 100644 >>>>> --- a/mm/mprotect.c >>>>> +++ b/mm/mprotect.c >>>>> @@ -152,6 +152,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, >>>>>                pages++; >>>>>            } else if (is_swap_pte(oldpte)) { >>>>>                swp_entry_t entry = pte_to_swp_entry(oldpte); >>>>> +            struct page *page = pfn_swap_entry_to_page(entry); >>>>>                pte_t newpte; >>>>>                  if (is_writable_migration_entry(entry)) { >>>> >>>> In change_pte_range(), is_writable_migration_entry() is not changed to !is_readable_migration_entry(). >>> >>> Yes, and also in change_huge_pmd(), is_writable_migration_entry() stays unchanged. >>> >>>> Is this done intentionally? Could you tell me why there's such a difference? I'm confused. It's very >>>> kind of you if you can answer my puzzle. >>> >>> For change protection, the only relevant part is to convert writable -> readable or writable -> readable_exclusive. >>> >>> If an entry is already readable or readable_exclusive, there is nothing to do. The only issues would be when turning a readable one into a readable_exclusive one or a readable_exclusive one into a readable one. >>> >>> >>> In hugetlb_change_protection(), the "!is_readable_migration_entry" could in fact be turned into a "is_writable_migration_entry()". Right now, it would convert writable -> readable or writable -> readable_exclusive AND readable -> readable AND readable_exclusive -> readable_exclusive, which isn't necessary but also shouldn't hurt either. >> >> Many thanks for your explanation. It's really helpful. :) >> >>> >>> >>> So yeah, it's not consistent but shouldn't be problematic. Do you see an issue with that? >> >> No, I don't see any issue with that. I just wonder whether we can change "!is_readable_migration_entry" to "is_writable_migration_entry()" to make code >> more consistent and avoid possible future puzzle. Also we can further remove this harmless unnecessary migration entry conversion. But this should >> be a separate cleanup patch anyway. > > Want to send a patch? :) Queued in my todo list. ;) Thanks! Miaohe Lin