linux-kernel - Re: [PATCH v9 10/11] mm/hugetlb: Gather discrete indexes of tail page

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Date:   Wed, 16 Dec 2020 15:03:40 +0100
From:   Oscar Salvador <osalvador@...e.de>
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,
        mhocko@...e.com, song.bao.hua@...ilicon.com, david@...hat.com,
        duanxiongchun@...edance.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v9 10/11] mm/hugetlb: Gather discrete indexes of tail page

On Sun, Dec 13, 2020 at 11:45:33PM +0800, Muchun Song wrote:
> For HugeTLB page, there are more metadata to save in the struct page.
> But the head struct page cannot meet our needs, so we have to abuse
> other tail struct page to store the metadata. In order to avoid
> conflicts caused by subsequent use of more tail struct pages, we can
> gather these discrete indexes of tail struct page. In this case, it
> will be easier to add a new tail page index later.
> 
> There are only (RESERVE_VMEMMAP_SIZE / sizeof(struct page)) struct
> page structs can be used when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP, so
"that can be..."

> add a BUILD_BUG_ON to catch invalid usage of the tail struct page.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>

I think this makes the current situation with metadata usage in sub-pages
easier to track.

Reviewed-by: Oscar Salvador <osalvador@...e.de>

-- 
Oscar Salvador
SUSE L3