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[2003:cb:c711:b800:254c:2d22:aab2:20a]) by smtp.gmail.com with ESMTPSA id 29sm935809ejk.107.2022.02.17.00.58.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Feb 2022 00:58:26 -0800 (PST) Message-ID: Date: Thu, 17 Feb 2022 09:58:26 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH v3 1/3] mm: enable MADV_DONTNEED for hugetlb mappings Content-Language: en-US To: Yin Fengwei , Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Naoya Horiguchi , Axel Rasmussen , Mina Almasry , Michal Hocko , Peter Xu , Andrea Arcangeli , Shuah Khan , Mike Rapoport , Andrew Morton References: <20220215002348.128823-1-mike.kravetz@oracle.com> <20220215002348.128823-2-mike.kravetz@oracle.com> <57fa170a-253b-932f-0261-b4905881d888@intel.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <57fa170a-253b-932f-0261-b4905881d888@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17.02.22 09:32, Yin Fengwei wrote: > > > On 2022/2/15 08:23, Mike Kravetz wrote: >> MADV_DONTNEED is currently disabled for hugetlb mappings. This >> certainly makes sense in shared file mappings as the pagecache maintains >> a reference to the page and it will never be freed. However, it could >> be useful to unmap and free pages in private mappings. In addition, >> userfaultfd minor fault users may be able to simplify code by using >> MADV_DONTNEED. >> >> The primary thing preventing MADV_DONTNEED from working on hugetlb >> mappings is a check in can_madv_lru_vma(). To allow support for hugetlb >> mappings create and use a new routine madvise_dontneed_free_valid_vma() >> that allows hugetlb mappings in this specific case. >> >> For normal mappings, madvise requires the start address be PAGE aligned >> and rounds up length to the next multiple of PAGE_SIZE. Do similarly > > In man page of mmap, NOTE for "Huge page (Huge TLB) mappings": > > "For munmap(), addr, and length must both be a multiple of the > underlying huge page size." > > Should we apply same rule to MADV_DONTNEED? Thanks. madvise() already has different rules than mmap() for ordinary pages, so we'd much rather try staying consistent with madvise() rules. -- Thanks, David / dhildenb