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Fri, 19 Mar 2021 05:16:34 -0700 (PDT) MIME-Version: 1.0 References: <20210315092015.35396-1-songmuchun@bytedance.com> <20210315092015.35396-8-songmuchun@bytedance.com> <20210319085948.GA5695@linux> In-Reply-To: <20210319085948.GA5695@linux> From: Muchun Song Date: Fri, 19 Mar 2021 20:15:58 +0800 Message-ID: Subject: Re: [External] Re: [PATCH v19 7/8] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap To: Oscar Salvador , David Hildenbrand Cc: Jonathan Corbet , Mike Kravetz , Thomas Gleixner , Ingo Molnar , bp@alien8.de, X86 ML , hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, Peter Zijlstra , Alexander Viro , 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 , Michal Hocko , "Song Bao Hua (Barry Song)" , =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= , Joao Martins , Xiongchun duan , linux-doc@vger.kernel.org, LKML , Linux Memory Management List , linux-fsdevel , Miaohe Lin , Chen Huang , Bodeddula Balasubramaniam Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: 3me43c1cnypzu14kb53z5he6wnmcdrrw X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 39F89801A813 Received-SPF: none (bytedance.com>: No applicable sender policy available) receiver=imf08; identity=mailfrom; envelope-from=""; helo=mail-pj1-f46.google.com; client-ip=209.85.216.46 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616156194-601414 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 Fri, Mar 19, 2021 at 4:59 PM Oscar Salvador wrote: > > On Mon, Mar 15, 2021 at 05:20:14PM +0800, Muchun Song wrote: > > --- 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() && !altmap) || > > + end - start < PAGES_PER_SECTION * sizeof(struct page)) > > err = vmemmap_populate_basepages(start, end, node, NULL); > > else if (boot_cpu_has(X86_FEATURE_PSE)) > > err = vmemmap_populate_hugepages(start, end, node, altmap); > > I've been thinking about this some more. > > Assume you opt-in the hugetlb-vmemmap feature, and assume you pass a valid altmap > to vmemmap_populate. > This will lead to use populating the vmemmap array with hugepages. Right. > > What if then, a HugeTLB gets allocated and falls within that memory range (backed > by hugetpages)? I am not sure whether we can allocate the HugeTLB pages from there. Will only device memory pass a valid altmap parameter to vmemmap_populate()? If yes, can we allocate HugeTLB pages from device memory? Sorry, I am not an expert on this. > AFAIK, this will get us in trouble as currently the code can only operate on memory > backed by PAGE_SIZE pages, right? > > I cannot remember, but I do not think nothing prevents that from happening? > Am I missing anything? Maybe David H is more familiar with this. Hi David, Do you have some suggestions on this? Thanks. > > -- > Oscar Salvador > SUSE L3