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[91.12.97.252]) by smtp.gmail.com with ESMTPSA id m4sm12020908wml.28.2021.09.24.02.36.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Sep 2021 02:36:47 -0700 (PDT) To: Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Michal Hocko , Oscar Salvador , Zi Yan , Muchun Song , Naoya Horiguchi , David Rientjes , "Aneesh Kumar K . V" , Andrew Morton References: <20210923175347.10727-1-mike.kravetz@oracle.com> <20210923175347.10727-3-mike.kravetz@oracle.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH v2 2/4] hugetlb: add HPageCma flag and code to free non-gigantic pages in CMA Message-ID: <7ab7690d-aa21-0fd9-75f1-f3a23b892853@redhat.com> Date: Fri, 24 Sep 2021 11:36:46 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210923175347.10727-3-mike.kravetz@oracle.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 4FC1A50000A6 X-Stat-Signature: hesj1zdqxsuknhppixe3g3364d9gaxp1 Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=MQKc2obO; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf04.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=david@redhat.com X-HE-Tag: 1632476213-876675 Content-Transfer-Encoding: quoted-printable 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 23.09.21 19:53, Mike Kravetz wrote: > When huge page demotion is fully implemented, gigantic pages can be > demoted to a smaller huge page size. For example, on x86 a 1G page > can be demoted to 512 2M pages. However, gigantic pages can potentiall= y > be allocated from CMA. If a gigantic page which was allocated from CMA > is demoted, the corresponding demoted pages needs to be returned to CMA= . >=20 > In order to track hugetlb pages that need to be returned to CMA, add th= e > hugetlb specific flag HPageCma. Flag is set when a huge page is > allocated from CMA and transferred to any demoted pages. Non-gigantic > huge page freeing code checks for the flag and takes appropriate action= . Do we really need that flag or couldn't we simply always try=20 cma_release() and fallback to out ordinary freeing-path? IIRC, cma knows exactly if something was allocated via a CMA are and can=20 be free via it. No need for additional tracking usually. --=20 Thanks, David / dhildenb