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(p200300cbc708f10080969368ba52a341.dip0.t-ipconnect.de. [2003:cb:c708:f100:8096:9368:ba52:a341]) by smtp.gmail.com with ESMTPSA id a7-20020a5d5087000000b0020e608186a5sm11741527wrt.48.2022.05.31.10.25.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 31 May 2022 10:25:12 -0700 (PDT) Message-ID: <3e4635bb-7c16-151a-d8ed-27742f0ae673@redhat.com> Date: Tue, 31 May 2022 19:25:11 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [RFC PATCH 3/3] hugetlb: Lazy page table copies in fork() To: Mike Kravetz , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Muchun Song , Michal Hocko , Peter Xu , Naoya Horiguchi , James Houghton , Mina Almasry , "Aneesh Kumar K . V" , Anshuman Khandual , Paul Walmsley , Christian Borntraeger , Andrew Morton References: <20220527225849.284839-1-mike.kravetz@oracle.com> <20220527225849.284839-4-mike.kravetz@oracle.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20220527225849.284839-4-mike.kravetz@oracle.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C1B491C0062 X-Stat-Signature: rfnaf61jpba33nqegogb87uiifredc6x X-Rspam-User: Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ORchVgbc; spf=none (imf20.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam08 X-HE-Tag: 1654017899-252206 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 28.05.22 00:58, Mike Kravetz wrote: > Lazy page table copying at fork time was introduced with commit > d992895ba2b2 ("Lazy page table copies in fork()"). At the time, > hugetlb was very new and did not support page faulting. As a result, > it was excluded. When full page fault support was added for hugetlb, > the exclusion was not removed. > > Simply remove the check that prevents lazy copying of hugetlb page > tables at fork. Of course, like other mappings this only applies to > shared mappings. > > Lazy page table copying at fork will be less advantageous for hugetlb > mappings because: > - There are fewer page table entries with hugetlb > - hugetlb pmds can be shared instead of copied > > In any case, completely eliminating the copy at fork time shold speed > things up. + make hugetlb less special, at least a tiny little bit Acked-by: David Hildenbrand -- Thanks, David / dhildenb