> -----Original Message-----
> From: owner-linux...@kvack.org [mailto:owner-linux...@kvack.org] On
> Behalf Of Oscar Salvador
> Sent: Tuesday, November 24, 2020 11:25 PM
> To: Muchun Song <songmuc...@bytedance.com>
> Cc: cor...@lwn.net; mike.krav...@oracle.com; t...@linutronix.de;
> mi...@redhat.com; b...@alien8.de; x...@kernel.org; h...@zytor.com;
> dave.han...@linux.intel.com; l...@kernel.org; pet...@infradead.org;
> v...@zeniv.linux.org.uk; a...@linux-foundation.org; paul...@kernel.org;
> mchehab+hua...@kernel.org; pawan.kumar.gu...@linux.intel.com;
> rdun...@infradead.org; oneu...@suse.com; anshuman.khand...@arm.com;
> jroe...@suse.de; almasrym...@google.com; rient...@google.com;
> wi...@infradead.org; mho...@suse.com; Song Bao Hua (Barry Song)
> <song.bao....@hisilicon.com>; duanxiongc...@bytedance.com;
> linux-...@vger.kernel.org; linux-kernel@vger.kernel.org; linux...@kvack.org;
> linux-fsde...@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
