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Mon, 25 Jan 2021 04:31:09 -0800 (PST) MIME-Version: 1.0 References: <20210117151053.24600-1-songmuchun@bytedance.com> <20210117151053.24600-10-songmuchun@bytedance.com> <7550ebba-fdb5-0dc9-a517-dda56bd105d9@redhat.com> In-Reply-To: <7550ebba-fdb5-0dc9-a517-dda56bd105d9@redhat.com> From: Muchun Song Date: Mon, 25 Jan 2021 20:30:32 +0800 Message-ID: Subject: Re: [External] Re: [PATCH v13 09/12] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap To: David Hildenbrand Cc: Jonathan Corbet , Mike Kravetz , Thomas Gleixner , mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, Peter Zijlstra , viro@zeniv.linux.org.uk, Andrew Morton , paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, Randy Dunlap , oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, Mina Almasry , David Rientjes , Matthew Wilcox , Oscar Salvador , Michal Hocko , "Song Bao Hua (Barry Song)" , =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= , Xiongchun duan , linux-doc@vger.kernel.org, LKML , Linux Memory Management List , linux-fsdevel Content-Type: text/plain; charset="UTF-8" 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 Mon, Jan 25, 2021 at 7:43 PM David Hildenbrand wrote: > > 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. Will update. Thanks. > > [...] > > > --- 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 for reminding me of this. Sorry I also did not notice that. > > -- > Thanks, > > David / dhildenb >