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s=arc-20220608; d=hostedemail.com; t=1701077077; a=rsa-sha256; cv=none; b=xWB+7RWfJ7ANoCZV6yfZtuWnzW1ztqaaooEluXPpoE9eCLCVvaIC4SrxcUmEuSbuRAfZqo pUeeOWBwKQLcWKLG6KRnSLSdtwMT4sVNh73226NwTGLdEfyJvxs1F4xnB71v0z8MXkgxnS e4N0QYhsDw8teJwMyQNmEqZG+HiUvlk= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=none; spf=pass (imf18.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com; dmarc=pass (policy=none) header.from=arm.com 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 EE1882F4; Mon, 27 Nov 2023 01:25:23 -0800 (PST) Received: from [10.57.73.191] (unknown [10.57.73.191]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1D3083F6C4; Mon, 27 Nov 2023 01:24:32 -0800 (PST) Message-ID: <755343a1-ce94-4d38-8317-0925e2dae3bc@arm.com> Date: Mon, 27 Nov 2023 09:24:31 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 01/14] mm: Batch-copy PTE ranges during fork() Content-Language: en-GB To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, andreyknvl@gmail.com, anshuman.khandual@arm.com, ardb@kernel.org, catalin.marinas@arm.com, david@redhat.com, dvyukov@google.com, glider@google.com, james.morse@arm.com, jhubbard@nvidia.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mark.rutland@arm.com, maz@kernel.org, oliver.upton@linux.dev, ryabinin.a.a@gmail.com, suzuki.poulose@arm.com, vincenzo.frascino@arm.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yuzenghui@huawei.com, yuzhao@google.com, ziy@nvidia.com References: <20231115163018.1303287-2-ryan.roberts@arm.com> <20231127055414.9015-1-v-songbaohua@oppo.com> From: Ryan Roberts In-Reply-To: <20231127055414.9015-1-v-songbaohua@oppo.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 9FBAF1C001B X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: mgd7ood469fin51tfs4myeoa36yk4hky X-HE-Tag: 1701077077-84734 X-HE-Meta: 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 SnaqRcC3 Rd3keFrBrmBrEWs2F/GG7zKWGYJoGQfvO2AAHJorZ5nmxJKfRtfy95CbeN5etoNyZu5p1pF3KHNobKHVy2QOHkVS3gC8a2IeTjfign47nUev7BRHFNG6MYbbC6cHGEP1iQKIaibuK/slWmYMqsDocGOs6egodNCZgF/1N5UjlJcOM8f5FAwlgYHO0SJifsPMhsm7PKkUY0BpZouXmXCxCFj8u0g== 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: On 27/11/2023 05:54, Barry Song wrote: >> +copy_present_ptes(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, >> + pte_t *dst_pte, pte_t *src_pte, >> + unsigned long addr, unsigned long end, >> + int *rss, struct folio **prealloc) >> { >> struct mm_struct *src_mm = src_vma->vm_mm; >> unsigned long vm_flags = src_vma->vm_flags; >> pte_t pte = ptep_get(src_pte); >> struct page *page; >> struct folio *folio; >> + int nr = 1; >> + bool anon; >> + bool any_dirty = pte_dirty(pte); >> + int i; >> >> page = vm_normal_page(src_vma, addr, pte); >> - if (page) >> + if (page) { >> folio = page_folio(page); >> - if (page && folio_test_anon(folio)) { >> - /* >> - * 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(page_try_dup_anon_rmap(page, false, 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); >> + anon = folio_test_anon(folio); >> + nr = folio_nr_pages_cont_mapped(folio, page, src_pte, addr, >> + end, pte, &any_dirty); > > in case we have a large folio with 16 CONTPTE basepages, and userspace > do madvise(addr + 4KB * 5, DONTNEED); nit: if you are offsetting by 5 pages from addr, then below I think you mean page0~page4 and page6~15? > > thus, the 4th basepage of PTE becomes PTE_NONE and folio_nr_pages_cont_mapped() > will return 15. in this case, we should copy page0~page3 and page5~page15. No I don't think folio_nr_pages_cont_mapped() will return 15; that's certainly not how its intended to work. The function is scanning forwards from the current pte until it finds the first pte that does not fit in the batch - either because it maps a PFN that is not contiguous, or because the permissions are different (although this is being relaxed a bit; see conversation with DavidH against this same patch). So the first time through this loop, folio_nr_pages_cont_mapped() will return 5, (page0~page4) then the next time through the loop we will go through the !present path and process the single swap marker. Then the 3rd time through the loop folio_nr_pages_cont_mapped() will return 10. Thanks, Ryan > > but the current code is copying page0~page14, right? unless we are immediatly > split_folio to basepages in zap_pte_range(), we will have problems? > >> + >> + for (i = 0; i < nr; i++, page++) { >> + if (anon) { >> + /* >> + * 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. >> + */ >> + if (unlikely(page_try_dup_anon_rmap( >> + page, false, src_vma))) { >> + if (i != 0) >> + break; >> + /* Page may be pinned, we have to copy. */ >> + return copy_present_page( >> + dst_vma, src_vma, dst_pte, >> + src_pte, addr, rss, prealloc, >> + page); >> + } >> + rss[MM_ANONPAGES]++; >> + VM_BUG_ON(PageAnonExclusive(page)); >> + } else { >> + page_dup_file_rmap(page, false); >> + rss[mm_counter_file(page)]++; >> + } > > Thanks > Barry >