linux-kernel - Re: [PATCH v4 05/21] mm/hugetlb: Introduce pgtable allocation/freeing helpers

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Message-ID: <20201117150604.GA15679@linux>
Date:   Tue, 17 Nov 2020 16:06:10 +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, 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 v4 05/21] mm/hugetlb: Introduce pgtable
 allocation/freeing helpers

On Fri, Nov 13, 2020 at 06:59:36PM +0800, Muchun Song wrote:
> +#define page_huge_pte(page)		((page)->pmd_huge_pte)

Seems you do not need this one anymore.

> +void vmemmap_pgtable_free(struct page *page)
> +{
> +	struct page *pte_page, *t_page;
> +
> +	list_for_each_entry_safe(pte_page, t_page, &page->lru, lru) {
> +		list_del(&pte_page->lru);
> +		pte_free_kernel(&init_mm, page_to_virt(pte_page));
> +	}
> +}
> +
> +int vmemmap_pgtable_prealloc(struct hstate *h, struct page *page)
> +{
> +	unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h);
> +
> +	/* Store preallocated pages on huge page lru list */
> +	INIT_LIST_HEAD(&page->lru);
> +
> +	while (nr--) {
> +		pte_t *pte_p;
> +
> +		pte_p = pte_alloc_one_kernel(&init_mm);
> +		if (!pte_p)
> +			goto out;
> +		list_add(&virt_to_page(pte_p)->lru, &page->lru);
> +	}

Definetely this looks better and easier to handle.
Btw, did you explore Matthew's hint about instead of allocating a new page,
using one of the ones you are going to free to store the ptes?
I am not sure whether it is feasible at all though.


> --- a/mm/hugetlb_vmemmap.h
> +++ b/mm/hugetlb_vmemmap.h
> @@ -9,12 +9,24 @@
>  #ifndef _LINUX_HUGETLB_VMEMMAP_H
>  #define _LINUX_HUGETLB_VMEMMAP_H
>  #include <linux/hugetlb.h>
> +#include <linux/mm.h>

why do we need this here?

-- 
Oscar Salvador
SUSE L3