Messages in this thread | | | From | "Song Bao Hua (Barry Song)" <> | Subject | RE: [PATCH v6 07/16] x86/mm/64: Disable PMD page mapping of vmemmap | Date | Tue, 24 Nov 2020 10:31:12 +0000 |
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> -----Original Message----- > From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org] On > Behalf Of Oscar Salvador > Sent: Tuesday, November 24, 2020 11:25 PM > To: Muchun Song <songmuchun@bytedance.com> > Cc: 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; mhocko@suse.com; Song Bao Hua (Barry Song) > <song.bao.hua@hisilicon.com>; duanxiongchun@bytedance.com; > linux-doc@vger.kernel.org; linux-kernel@vger.kernel.org; linux-mm@kvack.org; > linux-fsdevel@vger.kernel.org > Subject: Re: [PATCH v6 07/16] x86/mm/64: Disable PMD page mapping of > vmemmap > > On Tue, Nov 24, 2020 at 05:52:50PM +0800, Muchun Song wrote: > > If we enable the CONFIG_HUGETLB_PAGE_FREE_VMEMMAP, we can just > > disbale PMD page mapping of vmemmap to simplify the code. In this > > case, we do not need complex code doing vmemmap page table > > manipulation. This is a way to simply the first version of this > > patch series. In the future, we can add some code doing page table > > manipulation. > > IIRC, CONFIG_HUGETLB_PAGE_FREE_VMEMMAP was supposed to be enabled > by default, > right? > And we would control whether we __really__ want to this by a boot option, > which was disabled by default? > > If you go for populating the memmap with basepages by checking > CONFIG_HUGETLB_PAGE_FREE_VMEMMAP, would not everybody, even the > ones that > did not enable this by the boot option be affected? >
I would believe we could only bypass the pmd mapping of vmemmap while free_vmemmap is explicitly enabled. pmd mapping shouldn't be disabled in default. Would a cmdline of enabling vmemmap_free be used for the first patchset?
> -- > Oscar Salvador > SUSE L3
Thanks Barry
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