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 0C802C04A94 for ; Mon, 17 Jul 2023 13:22:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230372AbjGQNWQ (ORCPT ); Mon, 17 Jul 2023 09:22:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59536 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231563AbjGQNVs (ORCPT ); Mon, 17 Jul 2023 09:21:48 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3B510172E for ; Mon, 17 Jul 2023 06:21:37 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4D12BC15; Mon, 17 Jul 2023 06:22:20 -0700 (PDT) Received: from [10.57.76.30] (unknown [10.57.76.30]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EA5323F67D; Mon, 17 Jul 2023 06:21:33 -0700 (PDT) Message-ID: Date: Mon, 17 Jul 2023 14:21:31 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v3 1/4] mm: Non-pmd-mappable, large folios for folio_add_new_anon_rmap() To: David Hildenbrand , Andrew Morton , Matthew Wilcox , "Kirill A. Shutemov" , Yin Fengwei , Yu Zhao , Catalin Marinas , Will Deacon , Anshuman Khandual , Yang Shi , "Huang, Ying" , Zi Yan , Luis Chamberlain Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20230714160407.4142030-1-ryan.roberts@arm.com> <20230714161733.4144503-1-ryan.roberts@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/07/2023 14:19, David Hildenbrand wrote: > On 17.07.23 15:13, Ryan Roberts wrote: >> On 17/07/2023 14:00, David Hildenbrand wrote: >>> On 14.07.23 18:17, Ryan Roberts wrote: >>>> In preparation for FLEXIBLE_THP support, improve >>>> folio_add_new_anon_rmap() to allow a non-pmd-mappable, large folio to be >>>> passed to it. In this case, all contained pages are accounted using the >>>> order-0 folio (or base page) scheme. >>>> >>>> Signed-off-by: Ryan Roberts >>>> Reviewed-by: Yu Zhao >>>> Reviewed-by: Yin Fengwei >>>> --- >>>>    mm/rmap.c | 28 +++++++++++++++++++++------- >>>>    1 file changed, 21 insertions(+), 7 deletions(-) >>>> >>>> diff --git a/mm/rmap.c b/mm/rmap.c >>>> index 0c0d8857dfce..f293d072368a 100644 >>>> --- a/mm/rmap.c >>>> +++ b/mm/rmap.c >>>> @@ -1278,31 +1278,45 @@ void page_add_anon_rmap(struct page *page, struct >>>> vm_area_struct *vma, >>>>     * This means the inc-and-test can be bypassed. >>>>     * The folio does not have to be locked. >>>>     * >>>> - * If the folio is large, it is accounted as a THP.  As the folio >>>> + * If the folio is pmd-mappable, it is accounted as a THP.  As the folio >>>>     * is new, it's assumed to be mapped exclusively by a single process. >>>>     */ >>>>    void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct >>>> *vma, >>>>            unsigned long address) >>>>    { >>>> -    int nr; >>>> +    int nr = folio_nr_pages(folio); >>>> >>>> -    VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma); >>>> +    VM_BUG_ON_VMA(address < vma->vm_start || >>>> +            address + (nr << PAGE_SHIFT) > vma->vm_end, vma); >>>>        __folio_set_swapbacked(folio); >>>> >>>> -    if (likely(!folio_test_pmd_mappable(folio))) { >>>> +    if (!folio_test_large(folio)) { >>> >>> Why remove the "likely" here? The patch itself does not change anything about >>> that condition. >> >> Good question; I'm not sure why. Will have to put it down to bad copy/paste >> fixup. Will put it back in the next version. >> >>> >>>>            /* increment count (starts at -1) */ >>>>            atomic_set(&folio->_mapcount, 0); >>>> -        nr = 1; >>>> +        __page_set_anon_rmap(folio, &folio->page, vma, address, 1); >>>> +    } else if (!folio_test_pmd_mappable(folio)) { >>>> +        int i; >>>> + >>>> +        for (i = 0; i < nr; i++) { >>>> +            struct page *page = folio_page(folio, i); >>>> + >>>> +            /* increment count (starts at -1) */ >>>> +            atomic_set(&page->_mapcount, 0); >>>> +            __page_set_anon_rmap(folio, page, vma, >>>> +                    address + (i << PAGE_SHIFT), 1); >>>> +        } >>>> + >>>> +        /* increment count (starts at 0) */ >>> >>> That comment is a bit misleading. We're not talking about a mapcount as in the >>> other cases here. >> >> Correct, I'm talking about _nr_pages_mapped, which starts 0, not -1 like >> _mapcount. The comment was intended to be in the style used in other similar >> places in rmap.c. I could change it to: "_nr_pages_mapped is 0-based, so set it >> to the number of pages in the folio" or remove it entirely? What do you prefer? >> > > We only have to comment what's weird, not what's normal. > > IOW, we also didn't have such a comment in the existing code when doing > atomic_set(&folio->_nr_pages_mapped, COMPOUND_MAPPED); > > > What might make sense here is a simple > > "All pages of the folio are PTE-mapped." > ACK - thanks.