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(p200300cbc735040025015a2e13c688da.dip0.t-ipconnect.de. [2003:cb:c735:400:2501:5a2e:13c6:88da]) by smtp.gmail.com with ESMTPSA id f4-20020a5d4dc4000000b0031424f4ef1dsm19243672wru.19.2023.07.17.06.19.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 Jul 2023 06:19:43 -0700 (PDT) Message-ID: Date: Mon, 17 Jul 2023 15:19:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 To: Ryan Roberts , 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: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH v3 1/4] mm: Non-pmd-mappable, large folios for folio_add_new_anon_rmap() In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: C41D51C000C X-Rspam-User: X-Stat-Signature: hz3cubgp3kyoaj1penuiembkabqoajgz X-Rspamd-Server: rspam03 X-HE-Tag: 1689599987-99486 X-HE-Meta: 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 OYDc3JQB 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 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 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." -- Cheers, David / dhildenb