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[2003:cb:c74b:8b00:5520:fa3c:c527:592f]) by smtp.gmail.com with ESMTPSA id l24-20020a7bc458000000b003fbb25da65bsm21522971wmi.30.2023.08.16.08.11.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Aug 2023 08:11:55 -0700 (PDT) Message-ID: <2b6cc6b6-8fcb-35ff-3d5b-e4a6068847d9@redhat.com> Date: Wed, 16 Aug 2023 17:11:54 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v2 3/3] madvise:madvise_free_pte_range(): don't use mapcount() against large folio for sharing check To: Daniel Gomez , "Yin, Fengwei" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" , "akpm@linux-foundation.org" , "willy@infradead.org" , "vishal.moola@gmail.com" , "wangkefeng.wang@huawei.com" , "minchan@kernel.org" , "yuzhao@google.com" , "ryan.roberts@arm.com" , "shy828301@gmail.com" References: <20230808020917.2230692-1-fengwei.yin@intel.com> <20230808020917.2230692-4-fengwei.yin@intel.com> <4jvrmdpyteny5vaqmcrctzrovap2oy2zuukybbhfqyqbbb5xmy@ufgxufss2ngw> <2bfa1931-1fc6-5d6f-cba1-c7a9eb8a279a@intel.com> <4412ad3c-ebed-40a4-8f4e-83bb1b53b686@intel.com> From: David Hildenbrand Organization: Red Hat 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: 7bit X-Rspam-User: X-Stat-Signature: z3kss65mgpki8xnzzig7kyrrz7dx4zqy X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 650BF140151 X-HE-Tag: 1692198720-386519 X-HE-Meta: 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 fTFXMI4Y 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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 16.08.23 16:13, Daniel Gomez wrote: > On Wed, Aug 16, 2023 at 08:04:11PM +0800, Yin, Fengwei wrote: >> >> >> On 8/16/2023 7:44 PM, Daniel Gomez wrote: >>> On Wed, Aug 16, 2023 at 07:30:35AM +0800, Yin Fengwei wrote: >>>> >>>> >>>> On 8/15/23 21:25, Daniel Gomez wrote: >>>>> Hi Yin, >>>>> On Tue, Aug 08, 2023 at 10:09:17AM +0800, Yin Fengwei wrote: >>>>>> Commit 98b211d6415f ("madvise: convert madvise_free_pte_range() to use a >>>>>> folio") replaced the page_mapcount() with folio_mapcount() to check >>>>>> whether the folio is shared by other mapping. >>>>>> >>>>>> It's not correct for large folios. folio_mapcount() returns the total >>>>>> mapcount of large folio which is not suitable to detect whether the folio >>>>>> is shared. >>>>>> >>>>>> Use folio_estimated_sharers() which returns a estimated number of shares. >>>>>> That means it's not 100% correct. It should be OK for madvise case here. >>>>> >>>>> I'm trying to understand why it should be ok for madvise this change, so >>>>> I hope it's okay to ask you few questions. >>>>> >>>>> folio_mapcount() calculates the total maps for all the subpages of a >>>>> folio. However, the folio_estimated_sharers does it only for the first >>>>> subpage making it not true for large folios. Then, wouldn't this change >>>>> drop support for large folios? >>>> I saw David explained this very well in another mail. >>>> >>>>> >>>>> Seems like folio_entire_mapcount() is not accurate either because of it >>>>> does not inclue PTE-mapped sub-pages which I think we need here. Hence, >>>>> the folio_mapcount(). Could this be something missing in the test side? >>>>> >>>>> I tried to replicate the setup with CONFIG_TRANSPARENT_HUGEPAGE but >>>>> seems like I'm not able to do it: >>>>> >>>>> ./cow >>>>> # [INFO] detected THP size: 2048 KiB >>>>> # [INFO] detected hugetlb size: 2048 KiB >>>>> # [INFO] detected hugetlb size: 1048576 KiB >>>>> # [INFO] huge zeropage is enabled >>>>> TAP version 13 >>>>> 1..166 >>>>> # [INFO] Anonymous memory tests in private mappings >>>>> # [RUN] Basic COW after fork() ... with base page >>>>> not ok 1 MADV_NOHUGEPAGE failed >>>>> # [RUN] Basic COW after fork() ... with swapped out base page >>>>> not ok 2 MADV_NOHUGEPAGE failed >>>>> # [RUN] Basic COW after fork() ... with THP >>>>> not ok 3 MADV_HUGEPAGE failed >>>>> # [RUN] Basic COW after fork() ... with swapped-out THP >>>>> not ok 4 MADV_HUGEPAGE failed >>>>> # [RUN] Basic COW after fork() ... with PTE-mapped THP >>>>> not ok 5 MADV_HUGEPAGE failed >>>>> # [RUN] Basic COW after fork() ... with swapped-out, PTE-mapped THP >>>>> not ok 6 MADV_HUGEPAGE failed >>>>> ... >>>> Can you post the MADV_PAGEOUT and PTE-mapped THP related testing result? >>>> And I suppose swap need be enabled also for the testing. >>> >>> You may find a dump of the logs in the link below with system information. Let me >>> know if you find something wrong in my setup or if you need something else. >>> Besides CONFIG_TRANSPARENT_HUGEPAGE, CONFIG_SWAP is also enabled in the kernel. >>> >>> https://gitlab.com/-/snippets/2584135 >>> >>> Also, strace reports ENOSYS for MADV_*: >>> madvise(0x7f2912465000, 4096, MADV_NOHUGEPAGE) = -1 ENOSYS (Function not implemented) >>> madvise(0x7f2912000000, 2097152, MADV_HUGEPAGE) = -1 ENOSYS (Function not implemented) >> O. The problem here is MADV_HUGEPAGE/MADV_NOHUGEPAGE doesn't work. >> Do you have CONFIG_ADVISE_SYSCALLS enabled? > It worked after I enabled the conf. Some tests failed and some were > skipped. But I managed to reproduce the issue now, thanks Yin! > > Bail out! 4 out of 166 tests failed > # Totals: pass:146 fail:4 xfail:0 xpass:0 skip:16 error:0 > These hugetlb that are failing are known failures. -- Cheers, David / dhildenb