Re: [PATCH v17 2/9] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP

On Thu, Feb 25, 2021 at 09:21:23PM +0800, Muchun Song wrote:

The option HUGETLB_PAGE_FREE_VMEMMAP allows for the freeing of
some vmemmap pages associated with pre-allocated HugeTLB pages.
For example, on X86_64 6 vmemmap pages of size 4KB each can be
saved for each 2MB HugeTLB page. 4094 vmemmap pages of size 4KB
each can be saved for each 1GB HugeTLB page.

When a HugeTLB page is allocated or freed, the vmemmap array
representing the range associated with the page will need to be
remapped. When a page is allocated, vmemmap pages are freed
after remapping. When a page is freed, previously discarded
vmemmap pages must be allocated before remapping.

The config option is introduced early so that supporting code
can be written to depend on the option. The initial version of
the code only provides support for x86-64.

Like other code which frees vmemmap, this config option depends on
HAVE_BOOTMEM_INFO_NODE. The routine register_page_bootmem_info() is
used to register bootmem info. Therefore, make sure
register_page_bootmem_info is enabled if HUGETLB_PAGE_FREE_VMEMMAP
is defined.

Signed-off-by: Muchun Song <redacted>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Mike Kravetz <redacted>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
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Reviewed-by: Balbir Singh <bsingharora@gmail.com>