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Mon, 25 Jan 2021 11:43:30 +0000 (UTC) Received: from [10.36.115.13] (ovpn-115-13.ams2.redhat.com [10.36.115.13]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2BE4D19C44; Mon, 25 Jan 2021 11:43:24 +0000 (UTC) Subject: Re: [PATCH v13 09/12] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap To: Muchun Song , corbet@lwn.net, mike.kravetz@oracle.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, rdunlap@infradead.org, oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, almasrymina@google.com, rientjes@google.com, willy@infradead.org, osalvador@suse.de, mhocko@suse.com, song.bao.hua@hisilicon.com, naoya.horiguchi@nec.com Cc: duanxiongchun@bytedance.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org References: <20210117151053.24600-1-songmuchun@bytedance.com> <20210117151053.24600-10-songmuchun@bytedance.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <7550ebba-fdb5-0dc9-a517-dda56bd105d9@redhat.com> Date: Mon, 25 Jan 2021 12:43:23 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20210117151053.24600-10-songmuchun@bytedance.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 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 17.01.21 16:10, Muchun Song wrote: > Add a kernel parameter hugetlb_free_vmemmap to enable the feature of > freeing unused vmemmap pages associated with each hugetlb page on boot. The description completely lacks a description of the changes performed in arch/x86/mm/init_64.c. [...] > --- a/arch/x86/mm/init_64.c > +++ b/arch/x86/mm/init_64.c > @@ -34,6 +34,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -1557,7 +1558,8 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, > { > int err; > > - if (end - start < PAGES_PER_SECTION * sizeof(struct page)) > + if (is_hugetlb_free_vmemmap_enabled() || > + end - start < PAGES_PER_SECTION * sizeof(struct page)) This looks irresponsible. You ignore any altmap, even though current altmap users (ZONE_DEVICE) will not actually result in applicable vmemmaps that huge pages could ever use. Why do you ignore the altmap completely? This has to be properly documented, but IMHO it's not even the right approach to mess with altmap here. -- Thanks, David / dhildenb