Re: [External] Re: [PATCH v3 05/21] mm/hugetlb: Introduce pgtable allocation/freeing helpers

[Muchun Song <songmuchun@bytedance.com>]

On Fri, Nov 13, 2020 at 8:38 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 11/10/20 7:41 PM, Muchun Song wrote:
> > On Wed, Nov 11, 2020 at 8:47 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
> >>
> >> On 11/8/20 6:10 AM, Muchun Song wrote:
> >> I am reading the code incorrectly it does not appear page->lru (of the huge
> >> page) is being used for this purpose.  Is that correct?
> >>
> >> If it is correct, would using page->lru of the huge page make this code
> >> simpler?  I am just missing the reason why you are using
> >> page_huge_pte(page)->lru
> >
> > For 1GB HugeTLB pages, we should pre-allocate more than one page
> > table. So I use a linked list. The page_huge_pte(page) is the list head.
> > Because the page->lru shares storage with page->pmd_huge_pte.
>
> Sorry, but I do not understand the statement page->lru shares storage with
> page->pmd_huge_pte.  Are you saying they are both in head struct page of
> the huge page?
>
> Here is what I was suggesting.  If we just use page->lru for the list
> then vmemmap_pgtable_prealloc() could be coded like the following:
>
> static int vmemmap_pgtable_prealloc(struct hstate *h, struct page *page)
> {
>         struct page *pte_page, *t_page;
>         unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h);
>
>         if (!nr)
>                 return 0;
>
>         /* 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);
>         }
>
>         return 0;
> out:
>         list_for_each_entry_safe(pte_page, t_page, &page->lru, lru)
>                 pte_free_kernel(&init_mm, page_to_virt(pte_page));
>         return -ENOMEM;
> }
>
> By doing this we could eliminate the routines,
> vmemmap_pgtable_init()
> vmemmap_pgtable_deposit()
> vmemmap_pgtable_withdraw()
> and simply use the list manipulation routines.

Now I know what you mean. Yeah, just use page->lru can make code
simply. Thanks for your suggestions.

>
> To me, that looks simpler than the proposed code in this patch.
> --
> Mike Kravetz



-- 
Yours,
Muchun