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[2003:cb:c722:3700:6501:8925:6f9:fcdc]) by smtp.gmail.com with ESMTPSA id h6-20020a05600c350600b0040b43da0bbasm15709934wmq.30.2023.12.04.09.27.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 Dec 2023 09:27:10 -0800 (PST) Message-ID: <5b8b9f8c-8e9b-42a5-b8b2-9b96903f3ada@redhat.com> Date: Mon, 4 Dec 2023 18:27:08 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 01/15] mm: Batch-copy PTE ranges during fork() From: David Hildenbrand To: Ryan Roberts , Catalin Marinas , Will Deacon , Ard Biesheuvel , Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Zenghui Yu , Andrey Ryabinin , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , Andrew Morton , Anshuman Khandual , Matthew Wilcox , Yu Zhao , Mark Rutland , Kefeng Wang , John Hubbard , Zi Yan , Barry Song <21cnbao@gmail.com>, Alistair Popple , Yang Shi Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20231204105440.61448-1-ryan.roberts@arm.com> <20231204105440.61448-2-ryan.roberts@arm.com> <104de2d6-ecf9-4b0c-a982-5bd8e1aea758@redhat.com> Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: ACADF180035 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: d5bqsck943zfwregz7gn9adoqo1qd4r5 X-HE-Tag: 1701710834-449888 X-HE-Meta: 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 1d398PQ+ 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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: List-Subscribe: List-Unsubscribe: > > With rmap batching from [1] -- rebased+changed on top of that -- we could turn > that into an effective (untested): > > if (page && folio_test_anon(folio)) { > + nr = folio_nr_pages_cont_mapped(folio, page, src_pte, addr, end, > + pte, enforce_uffd_wp, &nr_dirty, > + &nr_writable); > /* > * If this page may have been pinned by the parent process, > * copy the page immediately for the child so that we'll always > * guarantee the pinned page won't be randomly replaced in the > * future. > */ > - folio_get(folio); > - if (unlikely(folio_try_dup_anon_rmap_pte(folio, page, src_vma))) { > + folio_ref_add(folio, nr); > + if (unlikely(folio_try_dup_anon_rmap_ptes(folio, page, nr, src_vma))) { > /* Page may be pinned, we have to copy. */ > - folio_put(folio); > - return copy_present_page(dst_vma, src_vma, dst_pte, src_pte, > - addr, rss, prealloc, page); > + folio_ref_sub(folio, nr); > + ret = copy_present_page(dst_vma, src_vma, dst_pte, > + src_pte, addr, rss, prealloc, > + page); > + return ret == 0 ? 1 : ret; > } > - rss[MM_ANONPAGES]++; > + rss[MM_ANONPAGES] += nr; > } else if (page) { > - folio_get(folio); > - folio_dup_file_rmap_pte(folio, page); > - rss[mm_counter_file(page)]++; > + nr = folio_nr_pages_cont_mapped(folio, page, src_pte, addr, end, > + pte, enforce_uffd_wp, &nr_dirty, > + &nr_writable); > + folio_ref_add(folio, nr); > + folio_dup_file_rmap_ptes(folio, page, nr); > + rss[mm_counter_file(page)] += nr; > } > > > We'll have to test performance, but it could be that we want to specialize > more on !folio_test_large(). That code is very performance-sensitive. > > > [1] https://lkml.kernel.org/r/20231204142146.91437-1-david@redhat.com So, on top of [1] without rmap batching but with a slightly modified version of yours (that keeps the existing code structure as pointed out and e.g., updates counter updates), running my fork() microbenchmark with a 1 GiB of memory: Compared to [1], with all order-0 pages it gets 13--14% _slower_ and with all PTE-mapped THP (order-9) it gets ~29--30% _faster_. So looks like we really want to have a completely seprate code path for "!folio_test_large()" to keep that case as fast as possible. And "Likely" we want to use "likely(!folio_test_large()". ;) Performing rmap batching on top of that code only slightly (another 1% or so) improves performance in the PTE-mapped THP (order-9) case right now, in contrast to other rmap batching. Reason is as all rmap code gets inlined here and we're only doing subpage mapcount updates + PAE handling. -- Cheers, David / dhildenb