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(p200300cbc704100021d5831de107fbd6.dip0.t-ipconnect.de. [2003:cb:c704:1000:21d5:831d:e107:fbd6]) by smtp.gmail.com with ESMTPSA id bp28-20020a5d5a9c000000b00273cd321a1bsm25937199wrb.107.2023.01.16.02.17.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Jan 2023 02:17:54 -0800 (PST) Message-ID: <06423461-c543-56fe-cc63-cabda6871104@redhat.com> Date: Mon, 16 Jan 2023 11:17:52 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH 21/46] hugetlb: use struct hugetlb_pte for walk_hugetlb_range To: Peter Xu , James Houghton Cc: Mike Kravetz , Muchun Song , David Rientjes , Axel Rasmussen , Mina Almasry , Zach O'Keefe , Manish Mishra , Naoya Horiguchi , "Dr . David Alan Gilbert" , "Matthew Wilcox (Oracle)" , Vlastimil Babka , Baolin Wang , Miaohe Lin , Yang Shi , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20230105101844.1893104-1-jthoughton@google.com> <20230105101844.1893104-22-jthoughton@google.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-Rspamd-Queue-Id: 3D3921C0002 X-Rspamd-Server: rspam01 X-Stat-Signature: dr7c1zbjr9b63z7hsdruykfguh4n3pn6 X-HE-Tag: 1673864278-875895 X-HE-Meta: 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 ufxzjz6Y dUZNem+81FhspCyQoXhCeVu821yTHDJAl2GYW0nrvFOKdXG8qMaPbMmX/eog1DiKlipMas4gsWGQKIqhGr+gTBo90KuCM9ArBjfFQ 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 12.01.23 22:33, Peter Xu wrote: > On Thu, Jan 12, 2023 at 04:17:52PM -0500, James Houghton wrote: >> I'll look into it, but doing it this way will use _mapcount, so we >> won't be able to use the vmemmap optimization. I think even if we do >> use Hugh's approach, refcount is still being kept on the head page, so >> there's still an overflow risk there (but maybe I am >> misunderstanding). > > Could you remind me what's the issue if using refcount on the small pages > rather than the head (assuming vmemmap still can be disabled)? The THP-way of doing things is refcounting on the head page. All folios use a single refcount on the head. There has to be a pretty good reason to do it differently. -- Thanks, David / dhildenb