linux-kernel - Re: [PATCH v9 03/11] mm/hugetlb: Free the vmemmap pages associated with each HugeTLB page

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Date:   Wed, 16 Dec 2020 14:06:07 +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 03/11] mm/hugetlb: Free the vmemmap pages associated
 with each HugeTLB page

On Sun, Dec 13, 2020 at 11:45:26PM +0800, Muchun Song wrote:
> +
> +/*
> + * vmemmap_rmap_walk - walk vmemmap page table
> + *
> + * @rmap_pte:		called for each non-empty PTE (lowest-level) entry.
> + * @reuse:		the page which is reused for the tail vmemmap pages.
> + * @vmemmap_pages:	the list head of the vmemmap pages that can be freed.
> + */
> +struct vmemmap_rmap_walk {
> +	void (*rmap_pte)(pte_t *pte, unsigned long addr,
> +			 struct vmemmap_rmap_walk *walk);
> +	struct page *reuse;
> +	struct list_head *vmemmap_pages;
> +};

Why did you chose this approach in this version?
Earlier versions of this patchset had a single vmemmap_to_pmd() function
which returned the PMD, and now we have serveral vmemmap_{levels}_range
and a vmemmap_rmap_walk.
A brief explanation about why this change was introduced would have been nice.

I guess it is because ealier versions were too oriented for the usecase
this patchset presents, while the new versions tries to be more broad
about future re-uses of the interface?


-- 
Oscar Salvador
SUSE L3