linux-kernel - Re: [PATCH v17 2/9] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE

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Message-ID: <20210304050619.GC1223287@balbir-desktop>
Date:   Thu, 4 Mar 2021 16:06:19 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     corbet@....net, mike.kravetz@...cle.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        paulmck@...nel.org, mchehab+huawei@...nel.org,
        pawan.kumar.gupta@...ux.intel.com, rdunlap@...radead.org,
        oneukum@...e.com, anshuman.khandual@....com, jroedel@...e.de,
        almasrymina@...gle.com, rientjes@...gle.com, willy@...radead.org,
        osalvador@...e.de, mhocko@...e.com, song.bao.hua@...ilicon.com,
        david@...hat.com, naoya.horiguchi@....com,
        joao.m.martins@...cle.com, duanxiongchun@...edance.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        Miaohe Lin <linmiaohe@...wei.com>
Subject: 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 <songmuchun@...edance.com>
> Reviewed-by: Oscar Salvador <osalvador@...e.de>
> Acked-by: Mike Kravetz <mike.kravetz@...cle.com>
> Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>
> ---

Reviewed-by: Balbir Singh <bsingharora@...il.com>